Three-dimensional memory device including discrete charge storage elements and methods of forming the same

ABSTRACT

An alternating stack of insulating layers and spacer material layers can be formed over a substrate. The spacer material layers may be formed as, or may be subsequently replaced with, electrically conductive layers. A memory opening can be formed through the alternating stack, and annular lateral recesses are formed at levels of the insulating layers. Metal portions are formed in the annular lateral recesses, and a semiconductor material layer is deposited over the metal portions. Metal-semiconductor alloy portions are formed by performing an anneal process, and are subsequently removed by performing a selective etch process. Remaining portions of the semiconductor material layer include a vertical stack of semiconductor material portions, which may be optionally converted, partly or fully, into silicon nitride material portions. The semiconductor material portions and/or the silicon nitride material portions can be employed as discrete charge storage elements.

FIELD

The present disclosure relates generally to the field of semiconductor devices, and particularly to a three-dimensional memory device including discrete charge storage elements and methods of manufacturing the same.

BACKGROUND

Three-dimensional vertical NAND strings having one bit per cell are disclosed in an article by T. Endoh et al., titled “Novel Ultra High Density Memory With A Stacked-Surrounding Gate Transistor (S-SGT) Structured Cell”, IEDM Proc. (2001) 33-36.

SUMMARY

According to an aspect of the present disclosure, a method of forming a three-dimensional memory device is provided, which comprises: forming an alternating stack of insulating layers and spacer material layers over a substrate, wherein the spacer material layers are formed as, or are subsequently replaced with, electrically conductive layer; forming a memory opening through the alternating stack; forming annular lateral recesses at levels of the insulating layers by laterally recessing sidewalls of the insulating layers relative to sidewalls of the spacer material layers around the memory opening; forming a vertical stack of discrete metal portions in the annular lateral recesses; forming a semiconductor material layer on the vertical stack of the metal portions; forming a vertical stack of metal-semiconductor alloy portions by reacting the vertical stack of metal portions with portions of the semiconductor material layer located at levels of the insulating layers; removing the vertical stack of metal-semiconductor alloy portions selective to unreacted portions of the semiconductor material layer, wherein unreacted portions of the semiconductor material layer remain at levels of the spacer material layers and comprise a vertical stack of discrete semiconductor material portions; and forming a tunneling dielectric layer and a vertical semiconductor channel in the memory opening.

According to another aspect of the present disclosure, a three-dimensional memory device is provided, which comprises: an alternating stack of insulating layers and electrically conductive layers located over a substrate; a memory opening vertically extending through the alternating stack, wherein the memory opening has laterally-protruding portions that extend outward at each level of the insulating layers; and a memory opening fill structure located in the memory opening and comprising, from outside to inside, a blocking dielectric layer, charge storage structures comprising a vertical stack of discrete semiconductor material portions and at least one silicon nitride material portion in contact with the vertical stack, a tunneling dielectric layer in contact with the charge storage structures, and a vertical semiconductor channel.

According to yet another aspect of the present disclosure, a three-dimensional memory device is provided, which comprises: an alternating stack of insulating layers and electrically conductive layers located over a substrate; a memory opening vertically extending through the alternating stack, wherein the memory opening has laterally-protruding portions that extend outward at levels of the insulating layers; and a memory opening fill structure located in the memory opening and comprising, from outside to inside, a blocking dielectric layer, a vertical stack of discrete charge storage material portions, a tunneling dielectric layer, and a vertical semiconductor channel, wherein each charge storage material portion comprises a tubular portion located at a level of a respective one of the electrically material layers, an upper flange portion laterally extending outward from an upper end of an outer sidewall of the tubular portion, and a lower flange portion laterally extending outward from a lower end of the outer sidewall of the tubular portion.

According to still another aspect of the present disclosure, a method of forming a three-dimensional memory device is provided, which comprises: forming an alternating stack of insulating layers and spacer material layers over a substrate, wherein the spacer material layers are formed as, or are subsequently replaced with, electrically conductive layer; forming a memory opening through the alternating stack; forming annular lateral recesses at levels of the insulating layers by laterally recessing sidewalls of the insulating layers relative to sidewalls of the spacer material layers around the memory opening; forming a vertical stack of discrete metal portions in the annular lateral recesses; forming a semiconductor material layer on the vertical stack of the metal portions; removing the vertical stack of discrete metal portions and portions of the semiconductor material layer that are adjacent to the vertical stack of discrete metal portions, wherein remaining portions of the semiconductor material layer comprise a vertical stack of semiconductor material portions, and each of the semiconductor material portions comprises a tubular portion, an upper flange portion laterally extending outward from an upper end of an outer sidewall of the tubular portion, and a lower flange portion laterally extending outward from a lower end of the outer sidewall of the tubular portion; and forming a tunneling dielectric layer and a vertical semiconductor channel in the memory opening.

According to another aspect of the present disclosure, a three-dimensional memory device is provided, which comprises: an alternating stack of insulating layers and electrically conductive layers located over a substrate; a memory opening vertically extending through the alternating stack, wherein the memory opening has laterally-protruding portions that extend outward at levels of the insulating layers; and a memory opening fill structure located in the memory opening and comprising, from outside to inside, a blocking dielectric layer, a vertical stack of charge storage material portions, a tunneling dielectric layer, and a vertical semiconductor channel, and a vertical stack of discrete annular insulating material portions located at the levels of the insulating layers between the blocking dielectric layer and the tunneling dielectric layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical cross-sectional view of an exemplary structure after formation of at least one peripheral device and a semiconductor material layer according to an embodiment of the present disclosure.

FIG. 2 is a schematic vertical cross-sectional view of the exemplary structure after formation of an alternating stack of insulating layers and sacrificial material layers according to an embodiment of the present disclosure.

FIG. 3 is a schematic vertical cross-sectional view of the exemplary structure after formation of stepped terraces and a retro-stepped dielectric material portion according to an embodiment of the present disclosure.

FIG. 4A is a schematic vertical cross-sectional view of the exemplary structure after formation of memory openings and support openings according to an embodiment of the present disclosure.

FIG. 4B is a top-down view of the exemplary structure of FIG. 4A. The vertical plane A-A′ is the plane of the cross-section for FIG. 4A.

FIGS. 5A-5P are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a first exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 5Q and 5R are sequential schematic vertical cross-sectional views of a memory opening during formation of an alternative configuration of the first exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 6A-6J are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a second exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 6K and 6L are sequential schematic vertical cross-sectional views of a memory opening during formation of an alternative configuration of the second exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 7A-7N are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a third exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 7O and 7P are sequential schematic vertical cross-sectional views of a memory opening during formation of an alternative configuration of the third exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 8A-8F are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a fourth exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 8G and 8H are sequential schematic vertical cross-sectional views of a memory opening during formation of an alternative configuration of the fourth exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 9A-9F are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a fifth exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 9G and 9H are sequential schematic vertical cross-sectional views of a memory opening during formation of an alternative configuration of the fifth exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 10A-10M are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a sixth exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 10N and 10O are sequential schematic vertical cross-sectional views of a memory opening during formation of an alternative configuration of the sixth exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 11A-11G are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a seventh exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 11H and 11I are sequential schematic vertical cross-sectional views of a memory opening during formation of an alternative configuration of the seventh exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 12A-12G are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of an eighth exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIGS. 12H and 12I are sequential schematic vertical cross-sectional views of a memory opening during formation of an alternative configuration of the eighth exemplary memory opening fill structure according to an embodiment of the present disclosure.

FIG. 13 is a schematic vertical cross-sectional view of the exemplary structure after formation of memory stack structures and support pillar structures according to an embodiment of the present disclosure.

FIG. 14A is a schematic vertical cross-sectional view of the exemplary structure after formation of backside trenches according to an embodiment of the present disclosure.

FIG. 14B is a partial see-through top-down view of the exemplary structure of FIG. 14A. The vertical plane A-A′ is the plane of the schematic vertical cross-sectional view of FIG. 14A.

FIG. 15 is a schematic vertical cross-sectional view of the exemplary structure after formation of backside recesses according to an embodiment of the present disclosure.

FIG. 16A is a schematic vertical cross-sectional view of the exemplary structure after formation of electrically conductive layers in the backside recesses according to an embodiment of the present disclosure.

FIG. 16B is a partial see-through top-down view of the exemplary structure of FIG. 16A. The vertical plane A-A′ is the plane of the schematic vertical cross-sectional view of FIG. 16A.

FIG. 17 is a schematic vertical cross-sectional view of the exemplary structure after formation of an insulating spacer and a backside contact structure according to an embodiment of the present disclosure.

FIG. 18A is a schematic vertical cross-sectional view of the exemplary structure after formation of additional contact via structures according to an embodiment of the present disclosure.

FIG. 18B is a top-down view of the exemplary structure of FIG. 18A. The vertical plane A-A′ is the plane of the schematic vertical cross-sectional view of FIG. 18A.

FIG. 19A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a first exemplary memory opening fill structure or a second exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 19B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the first exemplary memory opening fill structure or the second exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 20A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a third exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 20B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the third exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 21A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a fourth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 21B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the fourth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 22A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a fifth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 22B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the fifth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 23A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a sixth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 23B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the sixth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 24A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a seventh exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 24B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the seventh exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 25A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a eighth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

FIG. 25B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the eighth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

As discussed above, the present disclosure is directed to a three-dimensional memory device including discrete charge storage elements and methods of manufacturing the same, the various aspects of which are described below. The embodiments of the disclosure can be employed to form various structures including a multilevel memory structure, non-limiting examples of which include semiconductor devices such as three-dimensional monolithic memory array devices comprising a plurality of NAND memory strings.

The drawings are not drawn to scale. Multiple instances of an element may be duplicated where a single instance of the element is illustrated, unless absence of duplication of elements is expressly described or clearly indicated otherwise. Ordinals such as “first,” “second,” and “third” are employed merely to identify similar elements, and different ordinals may be employed across the specification and the claims of the instant disclosure. The term “at least one” element refers to all possibilities including the possibility of a single element and the possibility of multiple elements.

The same reference numerals refer to the same element or similar element. Unless otherwise indicated, elements having the same reference numerals are presumed to have the same composition and the same function. Unless otherwise indicated, a “contact” between elements refers to a direct contact between elements that provides an edge or a surface shared by the elements. If two or more elements are not in direct contact with each other or among one another, the two elements are “disjoined from” each other or “disjoined among” one another. As used herein, a first element located “on” a second element can be located on the exterior side of a surface of the second element or on the interior side of the second element. As used herein, a first element is located “directly on” a second element if there exist a physical contact between a surface of the first element and a surface of the second element. As used herein, a first element is “electrically connected to” a second element if there exists a conductive path consisting of at least one conductive material between the first element and the second element. As used herein, a “prototype” structure or an “in-process” structure refers to a transient structure that is subsequently modified in the shape or composition of at least one component therein.

As used herein, a “layer” refers to a material portion including a region having a thickness. A layer may extend over the entirety of an underlying or overlying structure, or may have an extent less than the extent of an underlying or overlying structure. Further, a layer may be a region of a homogeneous or inhomogeneous continuous structure that has a thickness less than the thickness of the continuous structure. For example, a layer may be located between any pair of horizontal planes between, or at, a top surface and a bottom surface of the continuous structure. A layer may extend horizontally, vertically, and/or along a tapered surface. A substrate may be a layer, may include one or more layers therein, or may have one or more layer thereupon, thereabove, and/or therebelow.

As used herein, a first surface and a second surface are “vertically coincident” with each other if the second surface overlies or underlies the first surface and there exists a vertical plane or a substantially vertical plane that includes the first surface and the second surface. A substantially vertical plane is a plane that extends straight along a direction that deviates from a vertical direction by an angle less than 5 degrees. A vertical plane or a substantially vertical plane is straight along a vertical direction or a substantially vertical direction, and may, or may not, include a curvature along a direction that is perpendicular to the vertical direction or the substantially vertical direction.

A monolithic three-dimensional memory array is a memory array in which multiple memory levels are formed above a single substrate, such as a semiconductor wafer, with no intervening substrates. The term “monolithic” means that layers of each level of the array are directly deposited on the layers of each underlying level of the array. In contrast, two dimensional arrays may be formed separately and then packaged together to form a non-monolithic memory device. For example, non-monolithic stacked memories have been constructed by forming memory levels on separate substrates and vertically stacking the memory levels, as described in U.S. Pat. No. 5,915,167 titled “Three-dimensional Structure Memory.” The substrates may be thinned or removed from the memory levels before bonding, but as the memory levels are initially formed over separate substrates, such memories are not true monolithic three-dimensional memory arrays. The various three-dimensional memory devices of the present disclosure include a monolithic three-dimensional NAND string memory device, and can be fabricated employing the various embodiments described herein.

Referring to FIG. 1, an exemplary structure according to an embodiment of the present disclosure is illustrated, which can be employed, for example, to fabricate a device structure containing vertical NAND memory devices. The exemplary structure includes a substrate (9, 10), which can be a semiconductor substrate. The substrate can include a lower substrate semiconductor layer 9 and an optional upper substrate semiconductor layer 10. The lower substrate semiconductor layer 9 may be a semiconductor wafer or a semiconductor material layer, and can include at least one elemental semiconductor material (e.g., single crystal silicon wafer or layer), at least one III-V compound semiconductor material, at least one II-VI compound semiconductor material, at least one organic semiconductor material, or other semiconductor materials known in the art. The substrate can have a major surface 7, which can be, for example, a topmost surface of the lower substrate semiconductor layer 9. The major surface 7 can be a semiconductor surface. In one embodiment, the major surface 7 can be a single crystalline semiconductor surface, such as a single crystalline semiconductor surface.

As used herein, a “semiconducting material” refers to a material having electrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0×10⁵ S/m. As used herein, a “semiconductor material” refers to a material having electrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0 S/m in the absence of electrical dopants therein, and is capable of producing a doped material having electrical conductivity in a range from 1.0 S/m to 1.0×10⁵ S/m upon suitable doping with an electrical dopant. As used herein, an “electrical dopant” refers to a p-type dopant that adds a hole to a valence band within a band structure, or an n-type dopant that adds an electron to a conduction band within a band structure. As used herein, a “conductive material” refers to a material having electrical conductivity greater than 1.0×10⁵ S/m. As used herein, an “insulator material” or a “dielectric material” refers to a material having electrical conductivity less than 1.0×10⁻⁵ S/m. As used herein, a “heavily doped semiconductor material” refers to a semiconductor material that is doped with electrical dopant at a sufficiently high atomic concentration to become a conductive material either as formed as a crystalline material or if converted into a crystalline material through an anneal process (for example, from an initial amorphous state), i.e., to have electrical conductivity greater than 1.0×10⁵ S/m. A “doped semiconductor material” may be a heavily doped semiconductor material, or may be a semiconductor material that includes electrical dopants (i.e., p-type dopants and/or n-type dopants) at a concentration that provides electrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0×10⁵ S/m. An “intrinsic semiconductor material” refers to a semiconductor material that is not doped with electrical dopants. Thus, a semiconductor material may be semiconducting or conductive, and may be an intrinsic semiconductor material or a doped semiconductor material. A doped semiconductor material can be semiconducting or conductive depending on the atomic concentration of electrical dopants therein. As used herein, a “metallic material” refers to a conductive material including at least one metallic element therein. All measurements for electrical conductivities are made at the standard condition.

At least one semiconductor device 700 for a peripheral circuitry can be formed on a portion of the lower substrate semiconductor layer 9. The at least one semiconductor device can include, for example, field effect transistors. For example, at least one shallow trench isolation structure 720 can be formed by etching portions of the lower substrate semiconductor layer 9 and depositing a dielectric material therein. A gate dielectric layer, at least one gate conductor layer, and a gate cap dielectric layer can be formed over the lower substrate semiconductor layer 9, and can be subsequently patterned to form at least one gate structure (750, 752, 754, 758), each of which can include a gate dielectric 750, a gate electrode (752, 754), and a gate cap dielectric 758. The gate electrode (752, 754) may include a stack of a first gate electrode portion 752 and a second gate electrode portion 754. At least one gate spacer 756 can be formed around the at least one gate structure (750, 752, 754, 758) by depositing and anisotropically etching a dielectric liner. Active regions 730 can be formed in upper portions of the lower substrate semiconductor layer 9, for example, by introducing electrical dopants employing the at least one gate structure (750, 752, 754, 758) as masking structures. Additional masks may be employed as needed. The active region 730 can include source regions and drain regions of field effect transistors. A first dielectric liner 761 and a second dielectric liner 762 can be optionally formed. Each of the first and second dielectric liners (761, 762) can comprise a silicon oxide layer, a silicon nitride layer, and/or a dielectric metal oxide layer. As used herein, silicon oxide includes silicon dioxide as well as non-stoichiometric silicon oxides having more or less than two oxygen atoms for each silicon atoms. Silicon dioxide is preferred. In an illustrative example, the first dielectric liner 761 can be a silicon oxide layer, and the second dielectric liner 762 can be a silicon nitride layer. The least one semiconductor device for the peripheral circuitry can contain a driver circuit for memory devices to be subsequently formed, which can include at least one NAND device.

A dielectric material such as silicon oxide can be deposited over the at least one semiconductor device, and can be subsequently planarized to form a planarization dielectric layer 770. In one embodiment the planarized top surface of the planarization dielectric layer 770 can be coplanar with a top surface of the dielectric liners (761, 762). Subsequently, the planarization dielectric layer 770 and the dielectric liners (761, 762) can be removed from an area to physically expose a top surface of the lower substrate semiconductor layer 9. As used herein, a surface is “physically exposed” if the surface is in physical contact with vacuum, or a gas phase material (such as air).

The optional upper substrate semiconductor layer 10, if present, can be formed on the top surface of the lower substrate semiconductor layer 9 prior to, or after, formation of the at least one semiconductor device 700 by deposition of a single crystalline semiconductor material, for example, by selective epitaxy. The deposited semiconductor material can be the same as, or can be different from, the semiconductor material of the lower substrate semiconductor layer 9. The deposited semiconductor material can be any material that can be employed for the lower substrate semiconductor layer 9 as described above. The single crystalline semiconductor material of the upper substrate semiconductor layer 10 can be in epitaxial alignment with the single crystalline structure of the lower substrate semiconductor layer 9. Portions of the deposited semiconductor material located above the top surface of the planarization dielectric layer 770 can be removed, for example, by chemical mechanical planarization (CMP). In this case, the upper substrate semiconductor layer 10 can have a top surface that is coplanar with the top surface of the planarization dielectric layer 770.

The region (i.e., area) of the at least one semiconductor device 700 is herein referred to as a peripheral device region 200. The region in which a memory array is subsequently formed is herein referred to as a memory array region 100. A staircase region 300 for subsequently forming stepped terraces of electrically conductive layers can be provided between the memory array region 100 and the peripheral device region 200.

In one alternative embodiment, the peripheral device region 200 may be located under the memory array region 100 in a CMOS under array configuration. In another alternative embodiment, the peripheral device region 200 may be located on a separate substrate which is subsequently bonded to the memory array region 100.

Referring to FIG. 2, a stack of an alternating plurality of insulating layers 32 and spacer material layers (which can be sacrificial material layers 42) is formed over the top surface of the substrate (9, 10). As used herein, a “material layer” refers to a layer including a material throughout the entirety thereof. As used herein, an alternating plurality of first elements and second elements refers to a structure in which instances of the first elements and instances of the second elements alternate. Each instance of the first elements that is not an end element of the alternating plurality is adjoined by two instances of the second elements on both sides, and each instance of the second elements that is not an end element of the alternating plurality is adjoined by two instances of the first elements on both ends. The first elements may have the same thickness thereamongst, or may have different thicknesses. The second elements may have the same thickness thereamongst, or may have different thicknesses. The alternating plurality of insulating layers 32 and spacer material layers may begin with a bottommost insulating layer 32 or with a bottommost spacer material layer, and may end with a topmost insulating layer 32 or with a topmost spacer material layer. In one embodiment, an instance of the first elements and an instance of the second elements may form a unit that is repeated with periodicity within the alternating plurality.

Generally, the spacer material layers may be formed as, or may be subsequently replaced with, electrically conductive layers. In case the spacer material layers are subsequently replaced with the electrically conductive layers, the spacer material layers are formed as sacrificial material layers 42. Alternatively, if the spacer material layers are formed as electrically conductive layers, replacement of the spacer material layers with other material layers is unnecessary. While the present disclosure is described employing an embodiment in which the spacer material layers are formed as sacrificial material layers 42 that are subsequently replaced with electrically conductive layers, embodiments are expressly contemplated herein in which the sacrificial material layers are formed as electrically conductive layers. In such cases, processing steps for replacing the sacrificial material layers 42 with electrically conductive layers are omitted.

The stack of the alternating plurality of the insulating layers 32 and the spacer material layers (such as the sacrificial material layers 42) is herein referred to as an alternating stack (32, 42). Insulating materials that can be employed for the insulating layers 32 include, but are not limited to, silicon oxide (including doped or undoped silicate glass), silicon nitride, silicon oxynitride, organosilicate glass (OSG), spin-on dielectric materials, dielectric metal oxides that are commonly known as high dielectric constant (high-k) dielectric oxides (e.g., aluminum oxide, hafnium oxide, etc.) and silicates thereof, dielectric metal oxynitrides and silicates thereof, and organic insulating materials. In one embodiment, the insulating material of the insulating layers 32 can be silicon oxide.

The spacer material of the sacrificial material layers 42 includes a sacrificial material that can be removed selective to the insulating material of the insulating layers 32. As used herein, a removal of a first material is “selective to” a second material if the removal process removes the first material at a rate that is at least twice the rate of removal of the second material. The ratio of the rate of removal of the first material to the rate of removal of the second material is herein referred to as a “selectivity” of the removal process for the first material with respect to the second material.

The sacrificial material layers 42 may comprise an insulating material, a semiconductor material, or a conductive material. The spacer material of the sacrificial material layers 42 can be subsequently replaced with electrically conductive electrodes which can function, for example, as control gate electrodes of a vertical NAND device. Non-limiting examples of the spacer material include silicon nitride, an amorphous semiconductor material (such as amorphous silicon), and a polycrystalline semiconductor material (such as polysilicon). In one embodiment, the sacrificial material layers 42 can be spacer material layers that comprise silicon nitride or a semiconductor material including at least one of silicon and germanium.

In one embodiment, the insulating layers 32 can include silicon oxide, and sacrificial material layers can include silicon nitride sacrificial material layers. The insulating material of the insulating layers 32 can be deposited, for example, by plasma enhanced chemical vapor deposition (PECVD). For example, if silicon oxide is employed for the insulating layers 32, tetraethyl orthosilicate (TEOS) can be employed as the precursor material for the PECVD process. The spacer material of the sacrificial material layers 42 can be formed, for example, by thermal CVD or atomic layer deposition (ALD).

The sacrificial material layers 42 can be suitably patterned so that conductive material portions to be subsequently formed by replacement of the sacrificial material layers 42 can function as electrically conductive electrodes, such as the control gate electrodes of the monolithic three-dimensional NAND string memory devices to be subsequently formed. The sacrificial material layers 42 may comprise a portion having a strip shape extending substantially parallel to the major surface 7 of the substrate.

The thicknesses of the insulating layers 32 and the sacrificial material layers 42 can be in a range from 20 nm to 50 nm, although lesser and greater thicknesses can be employed for each insulating layer 32 and for each sacrificial material layer 42. The number of repetitions of the pairs of an insulating layer 32 and a sacrificial material layer (e.g., a control gate electrode or a sacrificial material layer) 42 can be in a range from 2 to 1,024, and typically from 8 to 256, although a greater number of repetitions can also be employed. The top and bottom gate electrodes in the stack may function as the select gate electrodes. In one embodiment, each sacrificial material layer 42 in the alternating stack (32, 42) can have a uniform thickness that is substantially invariant within each respective sacrificial material layer 42.

Optionally, an insulating cap layer 70 can be formed over the alternating stack (32, 42). The insulating cap layer 70 includes a dielectric material that is different from the material of the sacrificial material layers 42. In one embodiment, the insulating cap layer 70 can include a dielectric material that can be employed for the insulating layers 32 as described above. The insulating cap layer 70 can have a greater thickness than each of the insulating layers 32. The insulating cap layer 70 can be deposited, for example, by chemical vapor deposition. In one embodiment, the insulating cap layer 70 can be a silicon oxide layer.

Referring to FIG. 3, stepped surfaces are formed at a peripheral region of the alternating stack (32, 42), which is herein referred to as a terrace region. As used herein, “stepped surfaces” refer to a set of surfaces that include at least two horizontal surfaces and at least two vertical surfaces such that each horizontal surface is adjoined to a first vertical surface that extends upward from a first edge of the horizontal surface, and is adjoined to a second vertical surface that extends downward from a second edge of the horizontal surface. A stepped cavity is formed within the volume from which portions of the alternating stack (32, 42) are removed through formation of the stepped surfaces. A “stepped cavity” refers to a cavity having stepped surfaces.

The terrace region is formed in the staircase region 300, which is located between the memory array region 100 and the peripheral device region 200 containing the at least one semiconductor device for the peripheral circuitry. The stepped cavity can have various stepped surfaces such that the horizontal cross-sectional shape of the stepped cavity changes in steps as a function of the vertical distance from the top surface of the substrate (9, 10). In one embodiment, the stepped cavity can be formed by repetitively performing a set of processing steps. The set of processing steps can include, for example, an etch process of a first type that vertically increases the depth of a cavity by one or more levels, and an etch process of a second type that laterally expands the area to be vertically etched in a subsequent etch process of the first type. As used herein, a “level” of a structure including alternating plurality is defined as the relative position of a pair of a first material layer and a second material layer within the structure.

Each sacrificial material layer 42 other than a topmost sacrificial material layer 42 within the alternating stack (32, 42) laterally extends farther than any overlying sacrificial material layer 42 within the alternating stack (32, 42) in the terrace region. The terrace region includes stepped surfaces of the alternating stack (32, 42) that continuously extend from a bottommost layer within the alternating stack (32, 42) to a topmost layer within the alternating stack (32, 42).

Each vertical step of the stepped surfaces can have the height of one or more pairs of an insulating layer 32 and a sacrificial material layer. In one embodiment, each vertical step can have the height of a single pair of an insulating layer 32 and a sacrificial material layer 42. In another embodiment, multiple “columns” of staircases can be formed along a first horizontal direction hd1 such that each vertical step has the height of a plurality of pairs of an insulating layer 32 and a sacrificial material layer 42, and the number of columns can be at least the number of the plurality of pairs. Each column of staircase can be vertically offset among one another such that each of the sacrificial material layers 42 has a physically exposed top surface in a respective column of staircases. In the illustrative example, two columns of staircases are formed for each block of memory stack structures to be subsequently formed such that one column of staircases provide physically exposed top surfaces for odd-numbered sacrificial material layers 42 (as counted from the bottom) and another column of staircases provide physically exposed top surfaces for even-numbered sacrificial material layers (as counted from the bottom). Configurations employing three, four, or more columns of staircases with a respective set of vertical offsets among the physically exposed surfaces of the sacrificial material layers 42 may also be employed. Each sacrificial material layer 42 has a greater lateral extent, at least along one direction, than any overlying sacrificial material layers 42 such that each physically exposed surface of any sacrificial material layer 42 does not have an overhang. In one embodiment, the vertical steps within each column of staircases may be arranged along the first horizontal direction hd1, and the columns of staircases may be arranged along a second horizontal direction hd2 that is perpendicular to the first horizontal direction hd1. In one embodiment, the first horizontal direction hd1 may be perpendicular to the boundary between the memory array region 100 and the staircase region 300.

A retro-stepped dielectric material portion 65 (i.e., an insulating fill material portion) can be formed in the stepped cavity by deposition of a dielectric material therein. For example, a dielectric material such as silicon oxide can be deposited in the stepped cavity. Excess portions of the deposited dielectric material can be removed from above the top surface of the insulating cap layer 70, for example, by chemical mechanical planarization (CMP). The remaining portion of the deposited dielectric material filling the stepped cavity constitutes the retro-stepped dielectric material portion 65. As used herein, a “retro-stepped” element refers to an element that has stepped surfaces and a horizontal cross-sectional area that increases monotonically as a function of a vertical distance from a top surface of a substrate on which the element is present. If silicon oxide is employed for the retro-stepped dielectric material portion 65, the silicon oxide of the retro-stepped dielectric material portion 65 may, or may not, be doped with dopants such as B, P, and/or F.

Optionally, drain select level isolation structures 72 (FIG. 4A) can be formed through the insulating cap layer 70 and a subset of the sacrificial material layers 42 located at drain select levels. The drain select level isolation structures 72 can be formed, for example, by forming drain select level isolation trenches and filling the drain select level isolation trenches with a dielectric material such as silicon oxide. Excess portions of the dielectric material can be removed from above the top surface of the insulating cap layer 70.

Referring to FIGS. 4A and 4B, a lithographic material stack (not shown) including at least a photoresist layer can be formed over the insulating cap layer 70 and the retro-stepped dielectric material portion 65, and can be lithographically patterned to form openings therein. The openings include a first set of openings formed over the memory array region 100 and a second set of openings formed over the staircase region 300. The pattern in the lithographic material stack can be transferred through the insulating cap layer 70 or the retro-stepped dielectric material portion 65, and through the alternating stack (32, 42) by at least one anisotropic etch that employs the patterned lithographic material stack as an etch mask. Portions of the alternating stack (32, 42) underlying the openings in the patterned lithographic material stack are etched to form memory openings 49 and support openings 19. As used herein, a “memory opening” refers to a structure in which memory elements, such as a memory stack structure, is subsequently formed. As used herein, a “support opening” refers to a structure in which a support structure (such as a support pillar structure) that mechanically supports other elements is subsequently formed. The memory openings 49 are formed through the insulating cap layer 70 and the entirety of the alternating stack (32, 42) in the memory array region 100. The support openings 19 are formed through the retro-stepped dielectric material portion 65 and the portion of the alternating stack (32, 42) that underlie the stepped surfaces in the staircase region 300.

The memory openings 49 extend through the entirety of the alternating stack (32, 42). The support openings 19 extend through a subset of layers within the alternating stack (32, 42). The chemistry of the anisotropic etch process employed to etch through the materials of the alternating stack (32, 42) can alternate to optimize etching of the materials in the alternating stack (32, 42). The anisotropic etch can be, for example, a series of reactive ion etches. The sidewalls of the memory openings 49 and the support openings 19 can be substantially vertical, or can be tapered. The patterned lithographic material stack can be subsequently removed, for example, by ashing.

The memory openings 49 and the support openings 19 can extend from the top surface of the alternating stack (32, 42) to at least the horizontal plane including the topmost surface of the upper substrate semiconductor layer 10. In one embodiment, an overetch into the upper substrate semiconductor layer 10 may be optionally performed after the top surface of the upper substrate semiconductor layer 10 is physically exposed at a bottom of each memory opening 49 and each support opening 19. The overetch may be performed prior to, or after, removal of the lithographic material stack. In other words, the recessed surfaces of the upper substrate semiconductor layer 10 may be vertically offset from the un-recessed top surfaces of the upper substrate semiconductor layer 10 by a recess depth. The recess depth can be, for example, in a range from 1 nm to 50 nm, although lesser and greater recess depths can also be employed. The overetch is optional, and may be omitted. If the overetch is not performed, the bottom surfaces of the memory openings 49 and the support openings 19 can be coplanar with the topmost surface of the upper substrate semiconductor layer 10.

Each of the memory openings 49 and the support openings 19 may include a sidewall (or a plurality of sidewalls) that extends substantially perpendicular to the topmost surface of the substrate. A two-dimensional array of memory openings 49 can be formed in the memory array region 100. A two-dimensional array of support openings 19 can be formed in the staircase region 300. The lower substrate semiconductor layer 9 and the upper substrate semiconductor layer 10 collectively constitutes a substrate (9, 10), which can be a semiconductor substrate. Alternatively, the upper substrate semiconductor layer 10 may be omitted, and the memory openings 49 and the support openings 19 can be extend to a top surface of the lower substrate semiconductor layer 9.

FIGS. 5A-5P illustrate structural changes in a memory opening 49 during formation of a first exemplary memory opening fill structure. The same structural change occurs simultaneously in each of the other memory openings 49 and in each of the support openings 19.

Referring to FIG. 5A, a memory opening 49 in the exemplary device structure of FIGS. 4A and 4B is illustrated. The memory opening 49 extends through the insulating cap layer 70, the alternating stack (32, 42), and optionally into an upper portion of the upper substrate semiconductor layer 10. At this processing step, each support opening 19 can extend through the retro-stepped dielectric material portion 65, a subset of layers in the alternating stack (32, 42), and optionally through the upper portion of the upper substrate semiconductor layer 10. The recess depth of the bottom surface of each memory opening with respect to the top surface of the upper substrate semiconductor layer 10 can be in a range from 0 nm to 30 nm, although greater recess depths can also be employed. Optionally, the sacrificial material layers 42 can be laterally recessed partially to form lateral recesses (not shown), for example, by an isotropic etch.

Referring to FIG. 5B, an optional pedestal channel portion (e.g., an epitaxial pedestal) 11 can be formed at the bottom portion of each memory opening 49 and each support openings 19, for example, by selective epitaxy. Each pedestal channel portion 11 comprises a single crystalline semiconductor material in epitaxial alignment with the single crystalline semiconductor material of the upper substrate semiconductor layer 10. In one embodiment, the top surface of each pedestal channel portion 11 can be formed above a horizontal plane including the top surface of a bottommost sacrificial material layer 42. In this case, a source select gate electrode can be subsequently formed by replacing the bottommost sacrificial material layer 42 with a conductive material layer. The pedestal channel portion 11 can be a portion of a transistor channel that extends between a source region to be subsequently formed in the substrate (9, 10) and a drain region to be subsequently formed in an upper portion of the memory opening 49. A memory cavity 49′ (FIG. 5D) is present in the unfilled portion of the memory opening 49 above the pedestal channel portion 11. In one embodiment, the pedestal channel portion 11 can comprise single crystalline silicon. In one embodiment, the pedestal channel portion 11 can have a doping of the first conductivity type, which is the same as the conductivity type of the upper substrate semiconductor layer 10 that the pedestal channel portion contacts. If an upper substrate semiconductor layer 10 is not present, the pedestal channel portion 11 can be formed directly on the lower substrate semiconductor layer 9, which can have a doping of the first conductivity type.

Referring to FIG. 5C, annular lateral recesses 149 can be formed at levels of the insulating layers 32 that are not masked by the pedestal channel portion 11. An additional annular lateral recess can be formed at the level of the insulating cap layer 70 around the memory opening 49. The annular lateral recesses 149 can be formed by laterally recessing sidewalls of the insulating layers 32 relative to sidewalls of the spacer material layers (such as the sacrificial material layers 42) around the memory opening 49. An isotropic etch process that etches the material of the insulating layers 32 selective to the material of the spacer material layers can be performed to laterally recess the physically exposed sidewalls of the insulating layers 32 relative to sidewalls of the spacer material layers (such as the sacrificial material layers). In one embodiment, the physically exposed surfaces of the insulating cap layer 70 may be isotropically recessed concurrently with formation of the annular lateral recesses 149. In an illustrative example, the insulating layers 32 include silicon oxide, the spacer material layers 42 include silicon nitride or a semiconductor material (such as polysilicon), and the isotropic etch process comprises a wet etch process employing dilute hydrofluoric acid.

The duration of the isotropic etch process can be selected such that the lateral recess distance of the annular lateral recesses 149 can be in a range from 5 nm to 100 nm, such as from 10 nm to 50 nm, although lesser and greater lateral recess distances can also be employed. The lateral recess distance refers to the lateral distance between a recessed sidewall of an insulating layer 32 relative to a sidewall of an immediately overlying spacer material layer (such as an immediately overlying sacrificial material layer 42) or relative to a sidewall of an immediately underlying spacer material layer. Each annular lateral recess 149 can have a volume of an annular cylinder, and is a portion of the memory opening 49. Thus, the memory opening 49 includes a vertical stack of annular lateral recesses 149 provided at levels of the insulating layers 32.

Referring to FIG. 5D, a blocking dielectric layer 52 can be conformally deposited on physically exposed surfaces of the insulating layers 32 and the spacer material layers (such as the sacrificial material layers 42). The blocking dielectric layer 52 can be deposited on the sidewalls of the insulating layers 32, annular horizontal surfaces of the insulating layers 32 overlying or underlying a respective one of the annular lateral recesses 149, sidewalls of the sacrificial material layers 42, a bottom surface of the memory opening 49 (which may be a top surface of a pedestal channel portion 11 or a top surface of the upper substrate semiconductor layer 10 if a pedestal channel portion is not employed), and physically exposed surfaces of the insulating cap layer 70.

The blocking dielectric layer 52 can include a single dielectric material layer or a stack of a plurality of dielectric material layers. In one embodiment, the blocking dielectric layer can include a dielectric metal oxide layer consisting essentially of a dielectric metal oxide. As used herein, a dielectric metal oxide refers to a dielectric material that includes at least one metallic element and at least oxygen. The dielectric metal oxide may consist essentially of the at least one metallic element and oxygen, or may consist essentially of the at least one metallic element, oxygen, and at least one non-metallic element such as nitrogen. In one embodiment, the blocking dielectric layer 52 can include a dielectric metal oxide having a dielectric constant greater than 7.9, i.e., having a dielectric constant greater than the dielectric constant of silicon nitride.

Non-limiting examples of dielectric metal oxides include aluminum oxide (Al₂O₃), hafnium oxide (HfO₂), lanthanum oxide (LaO₂), yttrium oxide (Y₂O₃), tantalum oxide (Ta₂O₅), silicates thereof, nitrogen-doped compounds thereof, alloys thereof, and stacks thereof. The dielectric metal oxide layer can be deposited, for example, by chemical vapor deposition (CVD), atomic layer deposition (ALD), pulsed laser deposition (PLD), liquid source misted chemical deposition, or a combination thereof. The thickness of the dielectric metal oxide layer can be in a range from 1 nm to 20 nm, although lesser and greater thicknesses can also be employed. The dielectric metal oxide layer can subsequently function as a dielectric material portion that blocks leakage of stored electrical charges to control gate electrodes. In one embodiment, the blocking dielectric layer 52 includes aluminum oxide. In one embodiment, the blocking dielectric layer 52 can include multiple dielectric metal oxide layers having different material compositions.

Alternatively or additionally, the blocking dielectric layer 52 can include a dielectric semiconductor compound such as silicon oxide, silicon oxynitride, silicon nitride, or a combination thereof. In one embodiment, the blocking dielectric layer 52 can include silicon oxide. In this case, the dielectric semiconductor compound of the blocking dielectric layer 52 can be formed by a conformal deposition method such as low pressure chemical vapor deposition, atomic layer deposition, or a combination thereof. The thickness of the dielectric semiconductor compound can be in a range from 1 nm to 20 nm, although lesser and greater thicknesses can also be employed.

The blocking dielectric layer 52 has a laterally-undulating vertical cross-sectional profile, and comprises laterally-protruding portions that laterally extend into the annular lateral recesses 149. The laterally-protruding portions of the blocking dielectric layer 52 can be located at the levels of the insulating layers 32. Outer sidewalls of the laterally-protruding portions of the blocking dielectric layer 52 contact sidewalls of the insulating layers 32, and annular horizontal surfaces of the laterally-protruding portions of the blocking dielectric layer 52 contact annular horizontal surfaces of the spacer material layers (such as the sacrificial material layers 42).

Referring to FIG. 5E, a metal layer 66L can be conformally deposited on the inner sidewalls of the blocking dielectric layer. The metal layer 66L can include any metal that can form a metal-semiconductor alloy such as a metal silicide. In one embodiment, the metal layer 66L can include at least one transition metal that can form a metal silicide. For example, the metal layer 66L can include tungsten, titanium, cobalt, molybdenum, platinum, nickel, and/or any other transition metal that forms a metal silicide upon reaction with silicon. The metal layer 66L can be deposited by a conformal deposition method such as a chemical vapor deposition process or an atomic layer deposition process. The thickness of the metal layer 66L can be in a range from 2 nm to 20 nm, such as from 4 nm to 10 nm, although lesser and greater thicknesses can also be employed. The thickness of the metal layer 66L may be less than, equal to, or greater than one half of the thickness of each insulating layer 32. Thus, the annular lateral recesses 149 may, or may not, have unfilled volumes after formation of the metal layer 66L.

Referring to FIG. 5F, an optional patterning film 47 can be anisotropically deposited to cover the insulating cap layer 70 and the topmost laterally-protruding portion of the metal layer 66L that overlies the topmost spacer material layer (such as the topmost sacrificial material layer 42). The patterning film 47 is deposited with high directionality, and thus, has a significantly greater thickness above the insulating cap layer 70 than at the bottom horizontal surface of the memory opening 49 (which may be the top surface of the pedestal channel portion 11). The patterning film 47 may be a film including amorphous carbon as a predominant component. For example, Advanced Patterning Film™ by Applied Materials Inc.™ may be employed for the patterning film 47. Alternatively, the patterning film 47 can be omitted.

Portions of the metal layer located 66L outside the annular lateral recesses 149 can be anisotropically etched by performing an anisotropic etch process. The anisotropic etch process can employ an etch chemistry that etches the material of the metal layer 66L selective to the patterning film 47 (if present), selective to the material of the spacer material layers 42, and selective to the material of the blocking dielectric layer 52 and/or to the material of the pedestal channel portion 11. The anisotropic etch process can employ a reactive ion etch process. Remaining portions of the metal layer 66L comprise the vertical stack of discrete metal portions 66. The discrete metal portions 66 can be formed within a respective one of the annular lateral recesses 149 of the memory opening 49. Thus, the vertical stack of discrete metal portions 66 can be formed in the annular lateral recesses 149. The vertical stack of discrete metal portions 66 is formed directly on portions of an inner sidewall of the blocking dielectric layer 52 located at levels of the insulating layers 32.

The discrete metal portions 66 may have a C-shaped (e.g., clam shaped) vertical cross-sectional profile having vertical portion connecting two horizontal portions if the thickness of the metal layer 66L is less than one half of the thickness of each insulating layer 32, or may have a rectangular vertical cross-sectional profile if the thickness of the metal layer 66L is greater than one half of the thickness of each insulating layer 32. In one embodiment, the discrete metal portion 66 can comprise, and/or can consist essentially of, tungsten, titanium, cobalt, molybdenum, platinum, nickel, and/or any other transition metal that forms a metal silicide upon reaction with silicon.

Referring to FIG. 5G, the patterning film 47 (if present) can be subsequently removed, for example, by ashing. If the patterning film 47 is omitted, then the discrete metal portion 66 at the level of the insulating cap layer 70 is also not present because it would be removed during the anisotropic etch process shown in FIG. 5F.

Referring to FIG. 5H, a semiconductor material layer 54L can be conformally deposited on the physically exposed surfaces of the vertical stack of the metal portions 66 and on the physically exposed surfaces of the blocking dielectric layer 52. The semiconductor material layer 54L includes a semiconductor material that can form a metal-semiconductor alloy with the material of the metal portions 66. For example, the semiconductor material layer 54L can include silicon and/or germanium. In one embodiment, the semiconductor material layer 54L can include amorphous silicon, polysilicon, germanium, and/or a silicon-germanium alloy. The thickness of the semiconductor material layer 54L can be selected such that the entirety of the vertical stack of discrete metal portions 66 can react with the semiconductor material of the semiconductor material layer 54L during a subsequent anneal process. In one embodiment, the semiconductor material layer 54L can have a thickness in a range from 2 nm to 20 nm, such as from 4 nm to 10 nm, although lesser and greater thicknesses can also be employed.

Referring to FIG. 5I, an anisotropic etch process can be performed to remove horizontal portions of the semiconductor material layer 54L and the metal layer 66L (if present) that overlie the insulating cap layer 70, and to remove a horizontal portion of the semiconductor material layer 54L located at the bottom of the memory opening 49 (such as the horizontal portion of the semiconductor material layer 54L located above the pedestal channel portion 11).

Referring to FIG. 5J, a thermal anneal process is performed at an elevated temperature that induces formation of a metal-semiconductor alloy between the material of the metal portions 66 and the material of the semiconductor material layer 54L. The elevated temperature may be in a range from 400 degrees Celsius to 1,000 degrees Celsius, although lower and higher temperatures may also be employed depending on the composition of the metal-semiconductor alloy. It is not necessary to form a low-resistance phase metal-semiconductor alloy as required for typical semiconductor applications in this case. Even high-resistance intermediate phase metal-semiconductor alloys formed at a relatively low temperature are sufficient provided that such metal-semiconductor alloys can be subsequently removed selective to unreacted portions of the semiconductor material layer 54L in a selective etch process. Generally, the thickness of the metal layer 66L and the thickness of the semiconductor material layer 54L can be selected to ensure that the entire volume of the metal portions 66 react with the semiconductor material layer 54L to form metal-semiconductor alloy portions 67. A vertical stack of metal-semiconductor alloy portions 67 can be formed by reacting the vertical stack of metal portions 66 with portions of the semiconductor material layer 54L located at levels of the insulating layers 32. Unreacted portions of the semiconductor material layer 54L remain at each level of the sacrificial material layers 42 located over the top surface of the pedestal channel portion 11. The set of unreacted portions of the semiconductor material layer 54L in the memory opening 49 comprise a vertical stack of semiconductor material portions 54S.

Referring to FIG. 5K, a selective isotropic etch process that etches the material of the metal-semiconductor alloy portions 67 selective to the material of the semiconductor material portions 54S can be performed. The vertical stack of metal-semiconductor alloy portions 67 is removed selective to unreacted portions of the semiconductor material layer 54L, i.e., the vertical stack of semiconductor material portions 54S. The vertical stack of semiconductor material portions 54S remain at levels of the spacer material layers (such as the sacrificial material layers 42). In one embodiment, each semiconductor portion 54S can have a have a tubular shape. As used herein, a “tubular” element refers to an element having an inner cylindrical sidewall, an outer cylindrical sidewall, and a substantially uniform thickness between the inner sidewall and the outer sidewall. The vertical stack of semiconductor material portions 54S can be subsequently employed as a vertical stack of charge storage elements, which can function as floating gates of a NAND string. Portions of the inner sidewall of the blocking dielectric layer 52 are physically exposed after removal of the vertical stack of metal-semiconductor alloy portions 67.

Referring to FIG. 5L, a tunneling dielectric layer 56 can be deposited employing a conformal deposition process such as a chemical vapor deposition process. The tunneling dielectric layer 56 includes a dielectric material through which charge tunneling can be performed under suitable electrical bias conditions. The tunneling dielectric layer 56 can be formed directly on the portions of the inner sidewall of the blocking dielectric layer 52 that are physically exposed and located at the levels of the insulating layers 32. The tunneling dielectric layer 56 can be formed directly on the vertical stack of discrete cylindrical semiconductor material portions 54S. The charge tunneling may be performed through hot-carrier injection or by Fowler-Nordheim tunneling induced charge transfer depending on the mode of operation of the monolithic three-dimensional NAND string memory device to be formed. The tunneling dielectric layer 56 can include silicon oxide, silicon nitride, silicon oxynitride, dielectric metal oxides (such as aluminum oxide and hafnium oxide), dielectric metal oxynitride, dielectric metal silicates, alloys thereof, and/or combinations thereof. In one embodiment, the tunneling dielectric layer 56 can include a stack of a first silicon oxide layer, a silicon oxynitride layer, and a second silicon oxide layer, which is commonly known as an ONO stack. In one embodiment, the tunneling dielectric layer 56 can include a silicon oxide layer that is substantially free of carbon or a silicon oxynitride layer that is substantially free of carbon. The thickness of the tunneling dielectric layer 56 can be in a range from 2 nm to 20 nm, although lesser and greater thicknesses can also be employed.

An optional first semiconductor channel layer 601 can be subsequently deposited on the tunneling dielectric layer 56 by a conformal deposition process. The first semiconductor channel layer 601 includes a semiconductor material such as at least one elemental semiconductor material, at least one III-V compound semiconductor material, at least one II-VI compound semiconductor material, at least one organic semiconductor material, or other semiconductor materials known in the art. In one embodiment, the first semiconductor channel layer 601 includes amorphous silicon or polysilicon. The first semiconductor channel layer 601 can be formed by a conformal deposition method such as low pressure chemical vapor deposition (LPCVD). The thickness of the first semiconductor channel layer 601 can be in a range from 2 nm to 10 nm, although lesser and greater thicknesses can also be employed.

Referring to FIG. 5M, an optional patterning film 77 can be anisotropically deposited to cover the insulating cap layer 70 and the topmost portion of the first semiconductor channel layer 601 that overlies the topmost spacer material layer (such as the topmost sacrificial material layer 42). The patterning film 77 is deposited with high directionality, and thus, has a significantly greater thickness above the insulating cap layer 70 than at the bottom horizontal surface of the memory opening 49 (which may be the top surface of the pedestal channel portion 11). The patterning film 77 may be a film including amorphous carbon as a predominant component. For example, Advanced Patterning Film™ by Applied Materials Inc.™ may be employed for the patterning film 77. Alternatively, the patterning film 77 may be omitted.

An anisotropic etch process can be performed to remove the horizontal bottom portions of the first semiconductor channel layer 601, the tunneling dielectric layer 56, and the blocking dielectric layer 52 located over the pedestal channel portion 11 (or located above the upper substrate semiconductor layer 10 in case a pedestal channel portion is not present) at the bottom of each memory opening 49. A center portion of the top surface of the pedestal channel portion 11 can be vertically recessed by the anisotropic etch process. In case a pedestal channel portion 11 is not present in the memory opening 49, a portion of the horizontal surface of the upper substrate semiconductor layer 10 can be vertically recessed underneath the memory opening 49. If present, the patterning film 77 can be subsequently removed, for example, by ashing.

A surface of the pedestal channel portion 11 (or a surface of the upper substrate semiconductor layer 10 in case the pedestal channel portions 11 are not employed) can be physically exposed underneath the opening through the first semiconductor channel layer 601, the tunneling dielectric layer 56, and the blocking dielectric layer 52. Optionally, the physically exposed semiconductor surface at the bottom of each memory cavity 49′ can be vertically recessed so that the recessed semiconductor surface underneath the memory cavity 49′ is vertically offset from the topmost surface of the pedestal channel portion 11 (or of the upper substrate semiconductor layer 10 in case pedestal channel portions 11 are not employed) by a recess distance. The vertical stack of semiconductor material portions 54S function as discrete charge storage elements that are floating gates. A set of the blocking dielectric layer 52, the vertical stack of semiconductor material portions 54S, and the tunneling dielectric layer 56 in a memory opening 49 constitutes a memory film 50. In one embodiment, the first semiconductor channel layer 601, the tunneling dielectric layer 56, and the blocking dielectric layer 52 can have vertically coincident sidewalls.

Referring to FIG. 5N, a second semiconductor channel layer 602 can be deposited directly on the semiconductor surface of the pedestal channel portion 11 or the upper substrate semiconductor layer 10 if the pedestal channel portion 11 is omitted, and directly on the first semiconductor channel layer 601 (if present). The second semiconductor channel layer 602 includes a semiconductor material such as at least one elemental semiconductor material, at least one III-V compound semiconductor material, at least one II-VI compound semiconductor material, at least one organic semiconductor material, or other semiconductor materials known in the art. In one embodiment, the second semiconductor channel layer 602 includes amorphous silicon or polysilicon. The second semiconductor channel layer 602 can be formed by a conformal deposition method such as low pressure chemical vapor deposition (LPCVD). The thickness of the second semiconductor channel layer 602 can be in a range from 2 nm to 10 nm, although lesser and greater thicknesses can also be employed. The second semiconductor channel layer 602 may partially fill the memory cavity 49′ in each memory opening, or may fully fill the cavity in each memory opening.

The materials of the first semiconductor channel layer 601 and the second semiconductor channel layer 602 are collectively referred to as a semiconductor channel material. In other words, the semiconductor channel material is a set of all semiconductor material in the first semiconductor channel layer 601 and the second semiconductor channel layer 602. The combination of the blocking dielectric layer 52, the tunneling dielectric layer 56, the first semiconductor channel layer 601, and the second semiconductor channel layer 602 can completely fill the volumes of the annular lateral recesses provided at the levels of the insulating layers 32.

Referring to FIG. 5O, in case the memory cavity 49′ in each memory opening is not completely filled by the second semiconductor channel layer 602, a dielectric core layer can be deposited in the memory cavity 49′ to fill any remaining portion of the memory cavity 49′ within each memory opening. The dielectric core layer includes a dielectric material such as silicon oxide or organosilicate glass. The dielectric core layer can be deposited by a conformal deposition method such as low pressure chemical vapor deposition (LPCVD), or by a self-planarizing deposition process such as spin coating. The horizontal portion of the dielectric core layer can be removed, for example, by a recess etch from above the top surface of the second semiconductor channel layer 602. Further, the material of the dielectric core layer can be vertically recessed selective to the semiconductor material of the second semiconductor channel layer 602 into each memory opening 49 down to a depth between a first horizontal plane including the top surface of the insulating cap layer 70 and a second horizontal plane including the bottom surface of the insulating cap layer 70. Each remaining portion of the dielectric core layer constitutes a dielectric core 62.

Referring to FIG. 5P, a doped semiconductor material having a doping of a second conductivity type can be deposited within each recessed region above the dielectric cores 62. The second conductivity type is the opposite of the first conductivity type. For example, if the first conductivity type is p-type, the second conductivity type is n-type, and vice versa. The dopant concentration of the doped semiconductor material can be in a range from 5.0×10¹⁸/cm³ to 2.0×10²¹/cm³, although lesser and greater dopant concentrations can also be employed. The doped semiconductor material can be, for example, doped polysilicon.

Excess portions of the deposited semiconductor material can be removed from above the top surface of the insulating cap layer 70, for example, by chemical mechanical planarization (CMP) or a recess etch. Each remaining portion of the semiconductor material having a doping of the second conductively type comprises a doped semiconductor region having a p-n junction at an interface with the vertical semiconductor channel 60. In one embodiment, the doped semiconductor region is employed as a drain region 63 for a vertical NAND string. The horizontal portion of the second semiconductor channel layer 602 located above the top surface of the insulating cap layer 70 can be concurrently removed by a planarization process. Each remaining portion of the second semiconductor channel layer 602 can be located entirety within a memory opening 49 or entirely within a support opening 19.

Each remaining portion of the doped semiconductor material having a doping of the second conductivity type constitutes a drain region 63. Each adjoining pair of the optional first semiconductor channel layer 601 and the second semiconductor channel layer 602 can collectively form a vertical semiconductor channel 60 through which electrical current can flow when a vertical NAND device including the vertical semiconductor channel 60 is turned on. A tunneling dielectric layer 56 is surrounded by a vertical stack of semiconductor material portions 54S, and laterally surrounds a portion of the vertical semiconductor channel 60. Each adjoining set of a tunneling dielectric layer 56, a vertical stack of semiconductor material portions 54S, and a blocking dielectric layer 52 collectively constitute a memory film 50, which includes a vertical stack of memory elements that can store a respective data bit with a macroscopic retention time. As used herein, a macroscopic retention time refers to a retention time suitable for operation of a memory device as a permanent memory device such as a retention time in excess of 24 hours.

Each combination of a memory film 50 and a vertical semiconductor channel 60 within a memory opening 49 constitutes a memory stack structure 55. The memory stack structure 55 is a combination of a semiconductor channel 60, a tunneling dielectric layer 56, a plurality of memory elements comprising a vertical stack of discrete (i.e., vertically separated from each other) semiconductor material portions 54S, and a blocking dielectric layer 52. Each combination of a pedestal channel portion 11 (if present), a memory stack structure 55, a dielectric core 62, and a drain region 63 within a memory opening 49 is herein referred to as a memory opening fill structure 58. Each combination of a pedestal channel portion 11 (if present), a memory film 50, a vertical semiconductor channel 60, a dielectric core 62, and a drain region 63 within each support opening 19 fills the respective support openings 19, and constitutes a support pillar structure.

FIGS. 5Q and 5R illustrate an alternative configuration of the first exemplary memory opening fill structure. Referring to FIG. 5Q, the alternative configuration of the first exemplary memory opening fill structure can be derived from the structure illustrated in FIG. 5K by filling the annular lateral recesses 149 with a dielectric fill material. Specifically, a dielectric fill material such as undoped silicate glass or a doped silicate glass can be deposited in the remaining volumes of the annular lateral recesses 149 after removal of the vertical stack of metal-semiconductor alloy portions 67. In one embodiment, the dielectric fill material may have a higher etch rate than the material of the blocking dielectric layer 52. For example, the dielectric fill material may include borosilicate glass, which can provide an etch rate in dilute hydrofluoric acid than the etch rate of undoped silicate glass by a factor in a range from 100 to 10,000.

Portions of the dielectric fill material can be removed from outside the annular lateral recesses 149 by etching back the dielectric fill material. An isotropic etch process or an anisotropic etch process may be employed. The chemistry of the etch process employed to etch the dielectric fill material can be selective to the material of the semiconductor material portions 54S and the material of the blocking dielectric layer 52. Remaining portions of the dielectric fill material filling the annular lateral recesses 149 comprise a vertical stack of annular insulating material portions 57. In case an anisotropic etch process is employed to pattern the annular insulating material portions 57, inner sidewalls of the annular insulating material portions 57 may be vertically coincident with inner sidewalls of the semiconductor material portions 54S.

Referring to FIG. 5R, the processing steps of FIGS. 5L-5P can be performed to provide an alternative configuration of the second exemplary memory opening fill structure 58. In this case, the tunneling dielectric layer 56 can be formed directly on the vertical stack of annular insulating material portions 57. The memory film 50 can comprise the blocking dielectric layer 52, the vertical stack of semiconductor material portions 54S, the vertical stack of annular insulating material portions 57 (which can contact the vertical stack of semiconductor material portions 54S), and the tunneling dielectric layer 56.

FIGS. 6A-6J are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a second exemplary memory opening fill structure according to an embodiment of the present disclosure. The second exemplary memory opening fill structure can be formed within each memory opening 49 in lieu of the first exemplary memory opening fill structure.

Referring to FIG. 6A, a memory opening 49 is illustrated during formation of the second exemplary memory opening fill structures in which the metal layer self-segregates into the annular lateral recesses 149 during an anneal. Specifically, the structure illustrated in FIG. 6A can be derived from the structure illustrated in FIG. 5D by conformally depositing a metal layer 166L on the inner sidewalls of the blocking dielectric layer 52. The metal layer 166L can include any metal that can spontaneously segregate into the annular lateral recesses 149 in a subsequent anneal process. For example, the metal layer 166L can include, and/or consist essentially of, cobalt.

Referring to FIG. 6B, a thermal anneal process is performed at an elevated temperature to induce thermal migration of the metal layer 166L into the annular lateral recesses 149. The metal layer 166L self-segregates into the vertical stack of discrete metal portions 166 during the thermal anneal process in order to reduce the total surface area. The elevated temperature of the thermal anneal process can be in a range from 300 degrees Celsius to 1,000 degrees Celsius, although lower and higher temperatures may also be employed depending on the composition of the metal layer 166L. The thickness of the metal layer 166L as deposited at the processing steps of FIG. 6A can be selected such that the discrete metal portions 166 are confined within a respective one of the annular lateral recesses 149, and are not in direct contact with each other (i.e., vertically separated from each other). Inner sidewalls of the blocking dielectric layer 52 can be physically exposed at each level of the spacer material layers (such as the sacrificial material layers 42).

Referring to FIG. 6C, the processing steps of FIG. 5H can be performed to form a semiconductor material layer 54L. The semiconductor material layer 54L can be conformally deposited over the physically exposed surfaces of the blocking dielectric layer 52 and the discrete metal portions 166, each of which may have an annular configuration.

Referring to FIG. 6D, a thermal anneal process is performed at an elevated temperature that induces formation of a metal-semiconductor alloy between the material of the metal portions 166 and the material of the semiconductor material layer 54L. The elevated temperature may be in a range from 400 degrees Celsius to 1,000 degrees Celsius, although lower and higher temperatures may also be employed depending on the composition of the metal-semiconductor alloy. Generally, the thickness of the metal layer 166L and the thickness of the semiconductor material layer 54L can be selected to ensure that the entire volume of the metal portions 166 react with the semiconductor material layer 54L to form metal-semiconductor alloy portions 167. A vertical stack of metal-semiconductor alloy portions 167 can be formed by reacting the vertical stack of metal portions 166 with portions of the semiconductor material layer 54L located at levels of the insulating layers 32. Unreacted portions of the semiconductor material layer 54L remain at each level of the sacrificial material layers 42 located over the top surface of the pedestal channel portion 11. The set of unreacted portions of the semiconductor material layer 54L in the memory opening 49 comprise a vertical stack of semiconductor material portions 54S.

Referring to FIG. 6E, a selective isotropic etch process that etches the material of the metal-semiconductor alloy portions 167 selective to the material of the semiconductor material portions 54S can be performed. The vertical stack of metal-semiconductor alloy portions 167 is removed selective to unreacted portions of the semiconductor material layer 54L, i.e., the vertical stack of semiconductor material portions 54S. The vertical stack of semiconductor material portions 54S remain at levels of the spacer material layers (such as the sacrificial material layers 42). In one embodiment, each semiconductor portion 54S can have a have a tubular shape. The vertical stack of semiconductor material portions 54S can be subsequently employed as a vertical stack of charge storage elements, which can function as floating gates of a NAND string. Portions of the inner sidewall of the blocking dielectric layer 52 are physically exposed after removal of the vertical stack of metal-semiconductor alloy portions 167.

Referring to FIG. 6F, the processing steps of FIG. 5L can be performed to form a tunneling dielectric layer 56 and a first semiconductor channel layer 601.

Referring to FIG. 6G, the processing steps of FIG. 5M can be performed to deposit an optional patterning film 77, and to anisotropically etch horizontal bottom portions of the first semiconductor channel layer 601, the tunneling dielectric layer 56, and the blocking dielectric layer 52 located over the pedestal channel portion 11 (or located above the upper substrate semiconductor layer 10 in case a pedestal channel portion is not present) at the bottom of each memory opening 49. A center portion of the top surface of the pedestal channel portion 11 can be vertically recessed by the anisotropic etch process. In case a pedestal channel portion 11 is not present in the memory opening 49, a portion of the horizontal surface of the upper substrate semiconductor layer 10 can be vertically recessed underneath the memory opening 49. The patterning film 77 (if present) can be subsequently removed, for example, by ashing.

Referring to FIG. 6H, the processing steps of FIG. 5N can be performed to form a second semiconductor channel layer 602. The materials of the first semiconductor channel layer 601 and the second semiconductor channel layer 602 are collectively referred to as a semiconductor channel material. The combination of the blocking dielectric layer 52, the tunneling dielectric layer 56, the first semiconductor channel layer 601, and the second semiconductor channel layer 602 can completely fill the volumes of the annular lateral recesses provided at the levels of the insulating layers 32.

Referring to FIG. 6I, the processing steps of FIG. 5O can be performed to form a dielectric core 62 in each memory opening 49.

Referring to FIG. 6J, the processing steps of FIG. 5P can be performed to form a doped semiconductor portion such as a drain region 63 at an upper portion of each memory opening 49. Each adjoining pair of a first semiconductor channel layer 601 (if present) and a second semiconductor channel layer 602 can collectively form a vertical semiconductor channel 60 through which electrical current can flow when a vertical NAND device including the vertical semiconductor channel 60 is turned on. A tunneling dielectric layer 56 is surrounded by a vertical stack of semiconductor material portions 54S, and laterally surrounds a portion of the vertical semiconductor channel 60. Each adjoining set of a tunneling dielectric layer 56, a vertical stack of semiconductor material portions 54S, and a blocking dielectric layer 52 collectively constitute a memory film 50, which includes a vertical stack of memory elements that can store a respective data bit with a macroscopic retention time.

Each combination of a memory film 50 and a vertical semiconductor channel 60 within a memory opening 49 constitutes a memory stack structure 55. The memory stack structure 55 is a combination of a semiconductor channel 60, a tunneling dielectric layer 56, a plurality of memory elements comprising a vertical stack of semiconductor material portions 54S, and a blocking dielectric layer 52. Each combination of a pedestal channel portion 11 (if present), a memory stack structure 55, a dielectric core 62, and a drain region 63 within a memory opening 49 is herein referred to as a memory opening fill structure 58. Each combination of a pedestal channel portion 11 (if present), a memory film 50, a vertical semiconductor channel 60, a dielectric core 62, and a drain region 63 within each support opening 19 fills the respective support openings 19, and constitutes a support pillar structure.

FIGS. 6K and 6L illustrate an alternative configuration of the second exemplary memory opening fill structure. Referring to FIG. 6K, the alternative configuration of the first exemplary memory opening fill structure can be derived from the structure illustrated in FIG. 6E by filling the annular lateral recesses 149 with a dielectric fill material. Specifically, a dielectric fill material such as undoped silicate glass or a doped silicate glass can be deposited in the remaining volumes of the annular lateral recesses 149 after removal of the vertical stack of metal-semiconductor alloy portions 67. In one embodiment, the dielectric fill material may have a higher etch rate than the material of the blocking dielectric layer 52. For example, the dielectric fill material may include borosilicate glass, which can provide an etch rate in dilute hydrofluoric acid than the etch rate of undoped silicate glass by a factor in a range from 100 to 10,000.

Portions of the dielectric fill material can be removed from outside the annular lateral recesses 149 by etching back the dielectric fill material. An isotropic etch process or an anisotropic etch process may be employed. The chemistry of the etch process employed to etch the dielectric fill material can be selective to the material of the semiconductor material portions 54S and the material of the blocking dielectric layer 52. Remaining portions of the dielectric fill material filling the annular lateral recesses 149 comprise a vertical stack of annular insulating material portions 57. In case an anisotropic etch process is employed to pattern the annular insulating material portions 57, inner sidewalls of the annular insulating material portions 57 may be vertically coincident with inner sidewalls of the semiconductor material portions 54S.

Referring to FIG. 6L, the processing steps of FIGS. 6F-6J can be performed to provide an alternative configuration of the second exemplary memory opening fill structure 58. In this case, the tunneling dielectric layer 56 can be formed directly on the vertical stack of annular insulating material portions 57. The memory film 50 can comprise the blocking dielectric layer 52, the vertical stack of semiconductor material portions 54S, the vertical stack of annular insulating material portions 57 (which can contact the vertical stack of semiconductor material portions 54S), and the tunneling dielectric layer 56.

FIGS. 7A-7N are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a third exemplary memory opening fill structure containing a hybrid charge storage structures containing a continuous charge storage dielectric layer and discrete floating gates, according to an embodiment of the present disclosure. The third exemplary memory opening fill structure can be formed within each memory opening 49 in lieu of the first or second exemplary memory opening fill structure described above.

Referring to FIG. 7A, a memory opening 49 is illustrated after formation of annular lateral recesses 149 at levels of the insulating layers 32. The exemplary structure of FIG. 7A may be the same as the exemplary structure illustrated in FIG. 5C.

Referring to FIG. 7B, the processing steps of FIG. 5D can be performed to form a blocking dielectric layer 52. Subsequently, a continuous charge storage dielectric layer, such as a silicon nitride layer 53, can be deposited on the physically exposed surfaces of the blocking dielectric layer 52 by a conformal deposition process such as a chemical vapor deposition process or an atomic layer deposition process. The silicon nitride layer 53 can have a thickness in a range from 1 nm to 8 nm, such as from 2 nm to 6 nm, although lesser and greater thicknesses can also be employed. The silicon nitride layer 53 vertically extends through layers of the alternating stack (32, 42), and contacts an outer sidewall of each discrete tubular semiconductor material portion 54S within the vertical stack of discrete tubular semiconductor material portions 54S. The silicon nitride layer 53 can be in contact with the inner sidewall of the blocking dielectric layer 52.

Referring to FIG. 7C, the processing steps of FIG. 5E can be performed to form a metal layer 66L directly on the silicon nitride layer 53.

Referring to FIG. 7D, the processing steps of FIG. 5F can optionally be performed to anisotropically deposit an optional patterning film 47, and to anisotropically etch portions of the metal layer 66L that are not masked by the patterning film 47. Remaining portions of the metal layer 66L after the anisotropic etch process include a vertical stack of discrete metal portions 66. Alternatively, if the metal layer 66L comprised cobalt, then it may be self-segregated into discrete metal portions 66 by an anneal as described with respect to FIG. 6B above.

Referring to FIG. 7E, the patterning film 47 (if present) can be subsequently removed, for example, by ashing.

Referring to FIG. 7F, the processing steps of FIG. 5H can be performed to conformally deposit a semiconductor material layer 54L.

Referring to FIG. 7G, the processing steps of FIG. 5I can be performed to anisotropically etch horizontal portions of the semiconductor material layer 54L and the metal layer 66L that overlie the insulating cap layer 70, and to remove a horizontal portion of the semiconductor material layer 54L located at the bottom of the memory opening 49 (such as the horizontal portion of the semiconductor material layer 54L located above the pedestal channel portion 11).

Referring to FIG. 7H, the processing steps of FIG. 5J can be performed. Specifically, a thermal anneal process is performed at an elevated temperature that induces formation of a metal-semiconductor alloy between the material of the metal portions 66 and the material of the semiconductor material layer 54L. Generally, the thickness of the metal layer 66L and the thickness of the semiconductor material layer 54L can be selected to ensure that the entire volume of the metal portions 66 react with the semiconductor material layer 54L to form metal-semiconductor alloy portions 67. A vertical stack of metal-semiconductor alloy portions 67 can be formed by reacting the vertical stack of metal portions 66 with portions of the semiconductor material layer 54L located at levels of the insulating layers 32. Unreacted portions of the semiconductor material layer 54L remain at each level of the sacrificial material layers 42 located over the top surface of the pedestal channel portion 11. The set of unreacted portions of the semiconductor material layer 54L in the memory opening 49 comprise a vertical stack of semiconductor material portions 54S.

Referring to FIG. 7I, the processing steps of 5K can be performed. Specifically, a selective isotropic etch process that etches the material of the metal-semiconductor alloy portions 67 selective to the material of the semiconductor material portions 54S can be performed. The vertical stack of metal-semiconductor alloy portions 67 is removed selective to unreacted portions of the semiconductor material layer 54L, i.e., the vertical stack of semiconductor material portions 54S. The vertical stack of semiconductor material portions 54S remain at levels of the spacer material layers (such as the sacrificial material layers 42). In one embodiment, each semiconductor portion 54S can have a have a tubular shape. The vertical stack of semiconductor material portions 54S can be subsequently employed as a vertical stack of charge storage elements, which can function as floating gates of a NAND string. Portions of the inner sidewall of the silicon nitride layer 53 are physically exposed after removal of the vertical stack of metal-semiconductor alloy portions 67.

Referring to FIG. 7J, the processing steps of FIG. 5L can be performed to form the tunneling dielectric layer 56 and the optional first semiconductor channel layer 601.

Referring to FIG. 7K, the processing steps of FIG. 5M can optionally be performed to anisotropically deposit a patterning film 77 over the insulating cap layer 70 and the topmost portion of the first semiconductor channel layer 601 that overlies the topmost spacer material layer (such as the topmost sacrificial material layer 42). An anisotropic etch process can be performed to remove the horizontal bottom portions of the first semiconductor channel layer 601, the tunneling dielectric layer 56, the silicon nitride layer 53, and the blocking dielectric layer 52 located over the pedestal channel portion 11 (or located above the upper substrate semiconductor layer 10 in case a pedestal channel portion is not present) at the bottom of each memory opening 49. A center portion of the top surface of the pedestal channel portion 11 can be vertically recessed by the anisotropic etch process. In case a pedestal channel portion 11 is not present in the memory opening 49, a portion of the horizontal surface of the upper substrate semiconductor layer 10 can be vertically recessed underneath the memory opening 49. The patterning film 77 can be subsequently removed, for example, by ashing.

A surface of the pedestal channel portion 11 (or a surface of the upper substrate semiconductor layer 10 in case the pedestal channel portions 11 are not employed) can be physically exposed underneath the opening through the first semiconductor channel layer 601, the tunneling dielectric layer 56, and the blocking dielectric layer 52. Optionally, the physically exposed semiconductor surface at the bottom of each memory cavity 49′ can be vertically recessed so that the recessed semiconductor surface underneath the memory cavity 49′ is vertically offset from the topmost surface of the pedestal channel portion 11 (or of the upper substrate semiconductor layer 10 in case pedestal channel portions 11 are not employed) by a recess distance. The vertical stack of semiconductor material portions 54S function as discrete charge storage elements that are floating gates. The continuous silicon nitride layer 53 functions as an additional charge storage material portion that continuously extends through each layer of the alternating stack (32, 42) located above the horizontal plane including the top surface of the pedestal channel portion 11. The combination of the silicon nitride layer 53 and the vertical stack of semiconductor material portions 54S constitute a composite charge storage structure including charge storage elements at each level of the spacer material layers (such as the sacrificial material layers 42). A set of the blocking dielectric layer 52, the silicon nitride layer 53, the vertical stack of semiconductor material portions 54S, and the tunneling dielectric layer 56 in a memory opening 49 constitutes a memory film 50. In one embodiment, the first semiconductor channel layer 601, the tunneling dielectric layer 56, the silicon nitride layer 53, and the blocking dielectric layer 52 can have vertically coincident sidewalls.

Referring to FIG. 7L, the processing steps of FIG. 5N can be performed to deposit a second semiconductor channel layer 602 directly on the semiconductor surface of the pedestal channel portion 11 or the upper substrate semiconductor layer 10 if the pedestal channel portion 11 is omitted, and directly on the first semiconductor channel layer 601. The combination of the blocking dielectric layer 52, the silicon nitride layer 53, the tunneling dielectric layer 56, the first semiconductor channel layer 601, and the second semiconductor channel layer 602 can completely fill the volumes of the annular lateral recesses provided at the levels of the insulating layers 32.

Referring to FIG. 7M, the processing steps of 5O can be performed a dielectric core 62 in each memory opening 49.

Referring to FIG. 7N, the processing steps of FIG. 5P can be performed to form a doped semiconductor material portion such as a drain region 63. Each adjoining pair of a first semiconductor channel layer 601 and a second semiconductor channel layer 602 can collectively form a vertical semiconductor channel 60 through which electrical current can flow when a vertical NAND device including the vertical semiconductor channel 60 is turned on. Each combination of a memory film 50 and a vertical semiconductor channel 60 within a memory opening 49 constitutes a memory stack structure 55. The memory stack structure 55 is a combination of a semiconductor channel 60, a tunneling dielectric layer 56, a plurality of memory elements comprising a vertical stack of semiconductor material portions 54S and portions of the silicon nitride layer 53 located at the levels of the spacer material layers 42, and a blocking dielectric layer 52. Each combination of a pedestal channel portion 11 (if present), a memory stack structure 55, a dielectric core 62, and a drain region 63 within a memory opening 49 is herein referred to as a memory opening fill structure 58. Each combination of a pedestal channel portion 11 (if present), a memory film 50, a vertical semiconductor channel 60, a dielectric core 62, and a drain region 63 within each support opening 19 fills the respective support openings 19, and constitutes a support pillar structure.

In one embodiment, the tunneling dielectric layer 56 has a laterally-undulating vertical cross-sectional profile, and comprises laterally-protruding portions located at levels of the insulating layers 32 and contacting horizontal annular surfaces of the blocking dielectric layer 52 and overlying or underlying portions of the spacer material layers (such as the sacrificial material layers 42) that are proximal to the vertical stack of discrete tubular semiconductor material portions 54S.

FIGS. 7O and 7P illustrate an alternative configuration of the third exemplary memory opening fill structure. Referring to FIG. 7O, the alternative configuration of the third exemplary memory opening fill structure can be derived from the structure illustrated in FIG. 7I by filling the annular lateral recesses 149 with a dielectric fill material. Specifically, a dielectric fill material such as undoped silicate glass or a doped silicate glass can be deposited in the remaining volumes of the annular lateral recesses 149 after removal of the vertical stack of metal-semiconductor alloy portions 67. In one embodiment, the dielectric fill material may have a higher etch rate than the material of the blocking dielectric layer 52. For example, the dielectric fill material may include borosilicate glass, which can provide an etch rate in dilute hydrofluoric acid than the etch rate of undoped silicate glass by a factor in a range from 100 to 10,000.

Portions of the dielectric fill material can be removed from outside the annular lateral recesses 149 by etching back the dielectric fill material. An isotropic etch process or an anisotropic etch process may be employed. The chemistry of the etch process employed to etch the dielectric fill material can be selective to the material of the semiconductor material portions 54S and the material of the blocking dielectric layer 52. Remaining portions of the dielectric fill material filling the annular lateral recesses 149 comprise a vertical stack of annular insulating material portions 57. In case an anisotropic etch process is employed to pattern the annular insulating material portions 57, inner sidewalls of the annular insulating material portions 57 may be vertically coincident with inner sidewalls of the semiconductor material portions 54S.

Referring to FIG. 7P, the processing steps of FIGS. 7J-7N can be performed to provide an alternative configuration of the third exemplary memory opening fill structure 58. In this case, the tunneling dielectric layer 56 can be formed directly on the vertical stack of annular insulating material portions 57. The memory film 50 can comprise the blocking dielectric layer 52, the silicon nitride layer 53, the vertical stack of semiconductor material portions 54S, the vertical stack of annular insulating material portions 57 (which can contact the vertical stack of semiconductor material portions 54S), and the tunneling dielectric layer 56.

The memory opening fill structure of FIG. 7P comprises a vertical stack of annular insulating material portions 57 located at each level of the insulating layers 32 between the blocking dielectric layer 52 and the tunneling dielectric layer 56. The tunneling dielectric layer 56 comprises a straight outer sidewall contacting each annular insulating material portion 57 within the vertical stack of annular insulating material portions 57 and contacting the vertical stack of discrete tubular semiconductor material portions 54S.

In the third exemplary memory opening fill structure 58 of FIG. 7N and the alternative embodiment of FIG. 7P, all surfaces of the vertical stack of discrete tubular semiconductor material portions 54S are in contact with a surface of the silicon nitride liner 53 or a surface of the tunneling dielectric layer 56.

The combination of the silicon nitride layer 53 and the vertical stack of discrete tubular semiconductor material portions 54S constitutes charge storage structures (53, 54S). Generally, the charge storage structures (53, 54S) comprises a vertical stack of discrete tubular semiconductor material portions 54S and at least one continuous silicon nitride material portion in contact with the vertical stack of discrete tubular semiconductor material portions 54S. In one embodiment, the at least one silicon nitride material portion comprises a silicon nitride layer 53 vertically extending through layers of the alternating stack (32, 42) and contacting an outer sidewall of each discrete tubular semiconductor material portion 54S within the vertical stack of discrete tubular semiconductor material portions 54S. In one embodiment shown in FIG. 7N, at the level of the insulating layers 32, the silicon nitride layer 53 is in contact with an inner sidewall of the blocking dielectric layer 52 and the outer sidewall of the tunneling dielectric layer 56. In one embodiment, all surfaces of the vertical stack of discrete tubular semiconductor material portions 54S can be in contact with a surface of the silicon nitride liner 53 or a surface of the tunneling dielectric layer 56.

FIGS. 8A-8F are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a fourth exemplary memory opening fill structure containing discrete charge storage dielectric portions according to an embodiment of the present disclosure. The fourth exemplary memory opening fill structure can be formed within each memory opening 49 in lieu of the first, second, or third exemplary memory opening fill structure described above.

Referring to FIG. 8A, the structure for forming a fourth exemplary memory opening fill structure can be derived from the structure of FIG. 5K, the structure of FIG. 6E, or the structure of FIG. 7I by nitriding the vertical stack of semiconductor material portions 54S. The vertical stack of semiconductor material portions 54S is at least partially converted into a vertical stack of silicon nitride material portions 54N, which may be a vertical stack of discrete tubular silicon nitride material portions 54N. In one embodiment, if the vertical stack of semiconductor material portions 54S completely converted into a vertical stack of silicon nitride material portions 54N, then each silicon nitride material portion 54N may have a graded silicon-to-nitrogen ratio with a lower ratio at the inner portion facing the memory opening 49 than at the outer portion facing the spacer material layers 42. In one embodiment, the thickness of each silicon nitride material portion 54N can be in a range from 3 nm to 30 nm, such as from 5 nm to 15 nm, although lesser and greater thicknesses can also be employed.

Referring to FIG. 8B, the processing steps of FIG. 5L can be performed to form the blocking dielectric layer 52 and an optional first semiconductor channel layer 601.

Referring to FIG. 8C, the processing steps of FIG. 5M can be performed to optionally deposit a patterning film 77, and to anisotropically etch horizontal bottom portions of the first semiconductor channel layer 601 (if present), the tunneling dielectric layer 56, and the blocking dielectric layer 52 located over the pedestal channel portion 11 (or located above the upper substrate semiconductor layer 10 in case a pedestal channel portion is not present) at the bottom of each memory opening 49. A center portion of the top surface of the pedestal channel portion 11 can be vertically recessed by the anisotropic etch process. In case a pedestal channel portion 11 is not present in the memory opening 49, a portion of the horizontal surface of the upper substrate semiconductor layer 10 can be vertically recessed underneath the memory opening 49. The patterning film 77 can be subsequently removed, for example, by ashing.

Referring to FIG. 8D, the processing steps of FIG. 5N can be performed to form a second semiconductor channel layer 602. The materials of the first semiconductor channel layer 601 and the second semiconductor channel layer 602 are collectively referred to as a semiconductor channel material. The combination of the blocking dielectric layer 52, the tunneling dielectric layer 56, the first semiconductor channel layer 601, and the second semiconductor channel layer 602 can completely fill the volumes of the annular lateral recesses provided at the levels of the insulating layers 32.

Referring to FIG. 8E, the processing steps of FIG. 5O can be performed to form a dielectric core 62 in each memory opening 49.

Referring to FIG. 8F, the processing steps of FIG. 5P can be performed to form a doped semiconductor portion such as a drain region 63 at an upper portion of each memory opening 49. Each adjoining pair of a first semiconductor channel layer 601 and a second semiconductor channel layer 602 can collectively form a vertical semiconductor channel 60 through which electrical current can flow when a vertical NAND device including the vertical semiconductor channel 60 is turned on. A tunneling dielectric layer 56 is surrounded by a vertical stack of silicon nitride material portions 54N, and laterally surrounds a portion of the vertical semiconductor channel 60. Each adjoining set of a tunneling dielectric layer 56, a vertical stack of silicon nitride material portions 54N, and a blocking dielectric layer 52 collectively constitute a memory film 50, which includes a vertical stack of memory elements that can store a respective data bit with a macroscopic retention time.

Each combination of a memory film 50 and a vertical semiconductor channel 60 within a memory opening 49 constitutes a memory stack structure 55. The memory stack structure 55 is a combination of a semiconductor channel 60, a tunneling dielectric layer 56, a plurality of memory elements comprising a vertical stack of silicon nitride material portions 54N, and a blocking dielectric layer 52. Each combination of a pedestal channel portion 11 (if present), a memory stack structure 55, a dielectric core 62, and a drain region 63 within a memory opening 49 is herein referred to as a memory opening fill structure 58. Each combination of a pedestal channel portion 11 (if present), a memory film 50, a vertical semiconductor channel 60, a dielectric core 62, and a drain region 63 within each support opening 19 fills the respective support openings 19, and constitutes a support pillar structure.

FIGS. 8G and 8H illustrate an alternative configuration of the fourth exemplary memory opening fill structure. Referring to FIG. 8G, the alternative configuration of the fourth exemplary memory opening fill structure can be derived from the structure illustrated in FIG. 8A by filling the annular lateral recesses 149 with a dielectric fill material. Specifically, a dielectric fill material such as undoped silicate glass or a doped silicate glass can be deposited in the remaining volumes of the annular lateral recesses 149 after removal of the vertical stack of metal-semiconductor alloy portions 67. In one embodiment, the dielectric fill material may have a higher etch rate than the material of the blocking dielectric layer 52. For example, the dielectric fill material may include borosilicate glass, which can provide an etch rate in dilute hydrofluoric acid than the etch rate of undoped silicate glass by a factor in a range from 100 to 10,000.

Portions of the dielectric fill material can be removed from outside the annular lateral recesses 149 by etching back the dielectric fill material. An isotropic etch process or an anisotropic etch process may be employed. The chemistry of the etch process employed to etch the dielectric fill material can be selective to the material of the silicon nitride material portions 54N and the material of the blocking dielectric layer 52. Remaining portions of the dielectric fill material filling the annular lateral recesses 149 comprise a vertical stack of annular insulating material portions 57. In case an anisotropic etch process is employed to pattern the annular insulating material portions 57, inner sidewalls of the annular insulating material portions 57 may be vertically coincident with inner sidewalls of the silicon nitride material portions 54N.

Referring to FIG. 8H, the processing steps of FIGS. 8B-8F can be performed to provide an alternative configuration of the first exemplary memory opening fill structure 58. In this case, the tunneling dielectric layer 56 can be formed directly on the vertical stack of annular insulating material portions 57. The memory film 50 can comprise the blocking dielectric layer 52, the vertical stack of silicon nitride material portions 54N, the vertical stack of annular insulating material portions 57 (which can contact the vertical stack of silicon nitride material portions 54N), and the tunneling dielectric layer 56.

FIGS. 9A-9F are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a fifth exemplary memory opening fill structure containing hybrid charge storage structures including discrete dielectric charge storage portions and floating gates, according to an embodiment of the present disclosure. The fifth exemplary memory opening fill structure can be formed within each memory opening 49 in lieu of the first, second, third, or fourth exemplary memory opening fill structure described above.

Referring to FIG. 9A, the structure for forming a fifth exemplary memory opening fill structure can be derived from the structure of FIG. 5K, the structure of FIG. 6E, or the structure of FIG. 7I by partially nitriding the vertical stack of semiconductor material portions 54S. A vertical stack of composite charge storage structures (54S, 54N) can be formed by converting surface portions of the vertical stack of discrete tubular semiconductor material portions 54S into silicon nitride material portions 54N. Each of the composite charge storage structures (54S, 54N) comprises a respective semiconductor material portion 54S which is a remaining portion of a respective one of the discrete tubular semiconductor material portions 54S and a respective silicon nitride material portion 54N which is formed by nitridation of a surface portion of the respective one of the discrete tubular semiconductor material portions 54S. In one embodiment, each silicon nitride material portion 54N comprises an interfacial region located in proximity to a respective one of the semiconductor material portions 54S and having a graded silicon-to-nitrogen ratio with decreases from portion 54N toward portion 54S. The thickness of each semiconductor material portion 54S can be in a range from 1 nm to 30 nm, such as from 2 nm to 20 nm, although lesser and greater thicknesses can also be employed. The thickness of each silicon nitride material portion 54N can be in a range from 1 nm to 30 nm, such as from 2 nm to 20 nm, although lesser and greater thicknesses can also be employed. The thickness of each composite charge storage structure (54S, 54N) can be in a range from 3 nm to 30 nm, such as from 5 nm to 15 nm, although lesser and greater thicknesses can also be employed.

Referring to FIG. 9B, the processing steps of FIG. 5L can be performed to form the blocking dielectric layer 52 and optionally the first semiconductor channel layer 601.

Referring to FIG. 9C, the processing steps of FIG. 5M can be performed to deposit a patterning film 77, and to anisotropically etch horizontal bottom portions of the first semiconductor channel layer 601, the tunneling dielectric layer 56, and the blocking dielectric layer 52 located over the pedestal channel portion 11 (or located above the upper substrate semiconductor layer 10 in case a pedestal channel portion is not present) at the bottom of each memory opening 49. A center portion of the top surface of the pedestal channel portion 11 can be vertically recessed by the anisotropic etch process. In case a pedestal channel portion 11 is not present in the memory opening 49, a portion of the horizontal surface of the upper substrate semiconductor layer 10 can be vertically recessed underneath the memory opening 49. The patterning film 77 can be subsequently removed, for example, by ashing.

Referring to FIG. 9D, the processing steps of FIG. 5N can be performed to form a second semiconductor channel layer 602. The materials of the first semiconductor channel layer 601 and the second semiconductor channel layer 602 are collectively referred to as a semiconductor channel material. The combination of the blocking dielectric layer 52, the tunneling dielectric layer 56, the first semiconductor channel layer 601, and the second semiconductor channel layer 602 can completely fill the volumes of the annular lateral recesses provided at the levels of the insulating layers 32.

Referring to FIG. 9E, the processing steps of FIG. 5O can be performed to form a dielectric core 62 in each memory opening 49.

Referring to FIG. 9F, the processing steps of FIG. 5P can be performed to form a doped semiconductor portion such as a drain region 63 at an upper portion of each memory opening 49. Each adjoining pair of a first semiconductor channel layer 601 and a second semiconductor channel layer 602 can collectively form a vertical semiconductor channel 60 through which electrical current can flow when a vertical NAND device including the vertical semiconductor channel 60 is turned on. A tunneling dielectric layer 56 is surrounded by a vertical stack of composite charge storage structures (54S, 54N), and laterally surrounds a portion of the vertical semiconductor channel 60. Each adjoining set of a tunneling dielectric layer 56, a vertical stack of composite charge storage structures (54S, 54N), and a blocking dielectric layer 52 collectively constitute a memory film 50, which includes a vertical stack of memory elements that can store a respective data bit with a macroscopic retention time.

Each combination of a memory film 50 and a vertical semiconductor channel 60 within a memory opening 49 constitutes a memory stack structure 55. The memory stack structure 55 is a combination of a semiconductor channel 60, a tunneling dielectric layer 56, a plurality of memory elements comprising a vertical stack of composite charge storage structures (54S, 54N), and a blocking dielectric layer 52. Each combination of a pedestal channel portion 11 (if present), a memory stack structure 55, a dielectric core 62, and a drain region 63 within a memory opening 49 is herein referred to as a memory opening fill structure 58. Each combination of a pedestal channel portion 11 (if present), a memory film 50, a vertical semiconductor channel 60, a dielectric core 62, and a drain region 63 within each support opening 19 fills the respective support openings 19, and constitutes a support pillar structure.

FIGS. 9G and 9H illustrate an alternative configuration of the fourth exemplary memory opening fill structure. Referring to FIG. 9G, the alternative configuration of the fourth exemplary memory opening fill structure can be derived from the structure illustrated in FIG. 9A by filling the annular lateral recesses 149 with a dielectric fill material. Specifically, a dielectric fill material such as undoped silicate glass or a doped silicate glass can be deposited in the remaining volumes of the annular lateral recesses 149 after removal of the vertical stack of metal-semiconductor alloy portions 67. In one embodiment, the dielectric fill material may have a higher etch rate than the material of the blocking dielectric layer 52. For example, the dielectric fill material may include borosilicate glass, which can provide an etch rate in dilute hydrofluoric acid than the etch rate of undoped silicate glass by a factor in a range from 100 to 10,000.

Portions of the dielectric fill material can be removed from outside the annular lateral recesses 149 by etching back the dielectric fill material. An isotropic etch process or an anisotropic etch process may be employed. The chemistry of the etch process employed to etch the dielectric fill material can be selective to the material of the composite charge storage structures (54S, 54N) and the material of the blocking dielectric layer 52. Remaining portions of the dielectric fill material filling the annular lateral recesses 149 comprise a vertical stack of annular insulating material portions 57. In case an anisotropic etch process is employed to pattern the annular insulating material portions 57, inner sidewalls of the annular insulating material portions 57 may be vertically coincident with inner sidewalls of the composite charge storage structures (54S, 54N).

Referring to FIG. 9H, the processing steps of FIGS. 9B-9F can be performed to provide an alternative configuration of the first exemplary memory opening fill structure 58. In this case, the tunneling dielectric layer 56 can be formed directly on the vertical stack of annular insulating material portions 57. The memory film 50 can comprise the blocking dielectric layer 52, the vertical stack of composite charge storage structures (54S, 54N), the vertical stack of annular insulating material portions 57 (which can contact the vertical stack of composite charge storage structures (54S, 54N)), and the tunneling dielectric layer 56.

FIGS. 10A-10M are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a sixth exemplary memory opening fill structure containing floating gates with flange portions according to an embodiment of the present disclosure. The sixth exemplary memory opening fill structure can be formed within each memory opening 49 in lieu of the first, second, third, fourth, or fifth exemplary memory opening fill structure described above.

Referring to FIG. 10A, a structure for forming a sixth exemplary memory opening fill structure is illustrated, which may be the same as the structure of FIG. 5D.

Referring to FIG. 10B, a metal layer 66L can be conformally deposited on the inner sidewalls of the blocking dielectric layer. The metal layer 66L can include any metal that can form a metal-semiconductor alloy such as a metal silicide. In one embodiment, the metal layer 66L can include at least one transition metal that can form a metal silicide. For example, the metal layer 66L can include tungsten, titanium, cobalt, molybdenum, platinum, nickel, and/or any other transition metal that forms a metal silicide upon reaction with silicon. The metal layer 66L can be deposited by a conformal deposition method such as a chemical vapor deposition process or an atomic layer deposition process. The thickness of the metal layer 66L may be greater than one half of the thickness of each insulating layer 32. In one embodiment, the metal layer fills an entire volume of each cavity in the annular lateral recesses 149. In one embodiment, the thickness of the metal layer 66L over sidewalls of the spacer material layers (such as the sacrificial material layers 42) can be in a range from 10 nm to 50, such as from 20 nm to 25 nm, although lesser and greater thicknesses can also be employed.

Referring to FIG. 10C, an optional anisotropic deposition process, such as a physical vapor deposition process (e.g., sputtering), may be optionally performed to deposit additional portions of the metal on horizontal surfaces of the metal layer 66L. Horizontal portions of the metal layer 66L can be thickened. The anisotropic metal deposition process increases the thickness of horizontal portions of the metal layer 66L so that removal of horizontal portions of a semiconductor material layer through formation of metal-semiconductor alloy portions is facilitated at a subsequent processing step. Alternatively, the step of FIG. 10C may be omitted.

Referring to FIG. 10D, an isotropic etch process such as a wet etch process can be performed to thin the metal layer 66L (i.e., to partially recess the metal layer 66L). Alternatively, if the metal layer 66L comprises cobalt, then the metal layer 66L may self-segregate during an anneal as described above to form the structure shown in FIG. 10D. Remaining portions of the metal layer 66L include vertical stack of discrete metal portions 66.

The discrete metal portions 66 can be formed within but not completely filling a respective one of the annular lateral recesses 149 of the memory opening 49. Each discrete metal portion 66 within the vertical stack of discrete metal portions 66 comprises an inner sidewall that is laterally offset outward from portions of an inner sidewall of the blocking dielectric layer 52 located at levels of the spacer material layers (such as the sacrificial material layers 42).

Thus, the vertical stack of discrete metal portions 66 can be formed in the annular lateral recesses 149. The vertical stack of discrete metal portions 66 is formed directly on portions of an inner sidewall of the blocking dielectric layer 52 located at levels of the insulating layers 32.

The discrete metal portions 66 may have a respective tubular shape. Each discrete metal portion 66 can have an inner sidewall that is laterally offset outward from sidewalls of the spacer material layers (such as the sacrificial material layers 42). In one embodiment, the discrete metal portion 66 can comprise, and/or can consist essentially of, tungsten, titanium, cobalt, molybdenum, platinum, nickel, and/or any other transition metal that forms a metal silicide upon reaction with silicon. In one embodiment, the discrete metal portions 66 can have a thickness in a range from 2 nm to 20 nm, such as from 4 nm to 10 nm, although lesser and greater thicknesses can also be employed. Horizontal remaining portions of the metal layer 66L may be present over the top surface of the pedestal channel portion 11 and over the top surface of the insulating cap layer 70.

Referring to FIG. 10E, a semiconductor material layer 54L can be conformally deposited on the physically exposed surfaces of the vertical stack of the metal portions 66 and on the physically exposed surfaces of the blocking dielectric layer 52. The semiconductor material layer 54L includes a semiconductor material that can form a metal-semiconductor alloy with the material of the metal portions 66. For example, the semiconductor material layer 54L can include silicon and/or germanium. In one embodiment, the semiconductor material layer 54L can include amorphous silicon, polysilicon, germanium, and/or a silicon-germanium alloy. The thickness of the semiconductor material layer 54L can be selected such that the entirety of the vertical stack of discrete metal portions 66 can react with the semiconductor material of the semiconductor material layer 54L during a subsequent anneal process. In one embodiment, the semiconductor material layer 54L can have a thickness in a range from 2 nm to 20 nm, such as from 4 nm to 10 nm, although lesser and greater thicknesses can also be employed.

Referring to FIG. 10F, a thermal anneal process is performed at an elevated temperature that induces formation of a metal-semiconductor alloy between the material of the metal portions 66 and the material of the semiconductor material layer 54L. The elevated temperature may be in a range from 400 degrees Celsius to 1,000 degrees Celsius, although lower and higher temperatures may also be employed depending on the composition of the metal-semiconductor alloy. It is not necessary to form a low-resistance phase metal-semiconductor alloy as required for typical semiconductor applications in this case. Even high-resistance intermediate phase metal-semiconductor alloys formed at a relatively low temperature is sufficient provided that such metal-semiconductor alloys can be subsequently removed selective to unreacted portions of the semiconductor material layer 54L in a selective etch process. Generally, the thickness of the discrete metal portions 66 and the thickness of the semiconductor material layer 54L can be selected to ensure that the entire volume of the metal portions 66 react with the semiconductor material layer 54L to form metal-semiconductor alloy portions 67. A vertical stack of metal-semiconductor alloy portions 67 can be formed by reacting the vertical stack of metal portions 66 with portions of the semiconductor material layer 54L located at levels of the insulating layers 32. Unreacted portions of the semiconductor material layer 54L remain at each level of the sacrificial material layers 42 located over the top surface of the pedestal channel portion 11. The set of unreacted portions of the semiconductor material layer 54L in the memory opening 49 comprise a vertical stack of semiconductor material portions 54S.

In one embodiment, the metal-semiconductor alloy portions 67 can be laterally offset outward from a cylindrical vertical plane including sidewalls of the spacer material layers (such as the sacrificial material layers 42) around the memory opening 49, while parts of the semiconductor material portions 54S protrude into the recesses 149. Specifically, each of the semiconductor material portions 54S comprises a tubular portion 54T, an upper flange portion 54U laterally extending outward into the recess 149 from an upper end of an outer sidewall of the tubular portion 54T, and a lower flange portion 54F laterally extending outward into the recess 149 from a lower end of the outer sidewall of the tubular portion 54T.

Referring to FIG. 10G, a selective isotropic etch process that etches the material of the metal-semiconductor alloy portions 67 selective to the material of the semiconductor material portions 54S can be performed. The vertical stack of metal-semiconductor alloy portions 67 is removed selective to unreacted portions of the semiconductor material layer 54L, i.e., the vertical stack of semiconductor material portions 54S. The vertical stack of semiconductor material portions 54S remain at levels of the spacer material layers (such as the sacrificial material layers 42) and extends partially into the recesses 149. In one embodiment, each of the semiconductor material portions 54S comprises a tubular portion 54T, an upper flange portion 54U, and a lower flange portion 54F. The upper flange portion 54U and the lower flange portion 54F of each semiconductor material portion 54S are located in the recess 149 and provide increased charge trapping volume in additional to the charge trapping volume provided by the tubular portion 54T. Thus, the thickness of the spacer material layers (such as the sacrificial material layers 42) can be reduced relative to conventional NAND devices in which charge storage elements do not include flange portions. The vertical stack of discrete semiconductor material portions 54S can be subsequently employed as a vertical stack of charge storage elements, which can function as floating gates of a NAND string. Portions of the inner sidewall of the blocking dielectric layer 52 are physically exposed after removal of the vertical stack of metal-semiconductor alloy portions 67. The vertical stack of discrete metal portions 66 and portions of the semiconductor material layer 54L that are adjacent to the vertical stack of discrete metal portions 66 are removed in the form of a vertical stack of metal-semiconductor alloy portions 67.

Referring to FIG. 10H, a tunneling dielectric layer 56 can be deposited employing a conformal deposition process such as a chemical vapor deposition process, as described in the previous embodiments. The tunneling dielectric layer 56 can be formed directly on the portions of the inner sidewall of the blocking dielectric layer 52 that are physically exposed and located at the levels of the insulating layers 32. The tunneling dielectric layer 56 can also be formed directly on the vertical stack of discrete cylindrical semiconductor material portions 54S. The combination of the blocking dielectric layer 52, the vertical stack of semiconductor material portions 54S, and the tunneling dielectric layer 56 constitutes a memory film 50.

Referring to FIG. 10I, the processing steps of FIG. 5L can be performed to form the optional first semiconductor channel layer 601 on the tunneling dielectric layer 56.

Referring to FIG. 10J, the processing steps of FIG. 5M can optionally be performed to deposit an optional patterning film 77. An anisotropic etch process can be performed to remove the horizontal bottom portions of the first semiconductor channel layer 601 (if present), the tunneling dielectric layer 56, and the blocking dielectric layer 52 located over the pedestal channel portion 11 (or located above the upper substrate semiconductor layer 10 in case a pedestal channel portion is not present) at the bottom of each memory opening 49. A set of the blocking dielectric layer 52, the vertical stack of semiconductor material portions 54S, and the tunneling dielectric layer 56 in a memory opening 49 constitutes a memory film 50. In one embodiment, the first semiconductor channel layer 601, the tunneling dielectric layer 56, and the blocking dielectric layer 52 can have vertically coincident sidewalls. The patterning film 77 (if present) can be subsequently removed, for example, by ashing.

Referring to FIG. 10K, the processing steps of FIG. 5N can be performed to deposit a second semiconductor channel layer 602. The materials of the first semiconductor channel layer 601 and the second semiconductor channel layer 602 are collectively referred to as a semiconductor channel material. In other words, the semiconductor channel material is a set of all semiconductor material in the first semiconductor channel layer 601 and the second semiconductor channel layer 602. The combination of flange portions of the semiconductor material portions 54S, the blocking dielectric layer 52, the tunneling dielectric layer 56, the first semiconductor channel layer 601, and the second semiconductor channel layer 602 can completely fill the volumes of the annular lateral recesses 149 provided at the levels of the insulating layers 32.

Referring to FIG. 10L, the processing steps of FIG. 5O can be performed to form a dielectric core 62.

Referring to FIG. 10M, the processing steps of FIG. 5P can be performed to form a doped semiconductor material portion such as a drain region 63. Each adjoining set of a tunneling dielectric layer 56, a vertical stack of semiconductor material portions 54S, and a blocking dielectric layer 52 collectively constitute a memory film 50, which includes a vertical stack of memory elements that can store a respective data bit with a macroscopic retention time. Each combination of a memory film 50 and a vertical semiconductor channel 60 within a memory opening 49 constitutes a memory stack structure 55. The memory stack structure 55 is a combination of a semiconductor channel 60, a tunneling dielectric layer 56, a plurality of memory elements comprising a vertical stack of semiconductor material portions 54S, and a blocking dielectric layer 52. Each combination of a pedestal channel portion 11 (if present), a memory stack structure 55, a dielectric core 62, and a drain region 63 within a memory opening 49 is herein referred to as a memory opening fill structure 58. Each combination of a pedestal channel portion 11 (if present), a memory film 50, a vertical semiconductor channel 60, a dielectric core 62, and a drain region 63 within each support opening 19 fills the respective support openings 19, and constitutes a support pillar structure.

FIGS. 10N and 10O illustrate an alternative configuration of the first exemplary memory opening fill structure. Referring to FIG. 10N, the alternative configuration of the first exemplary memory opening fill structure can be derived from the structure illustrated in FIG. 10G by filling the annular lateral recesses 149 with a dielectric fill material. Specifically, a dielectric fill material such as undoped silicate glass or a doped silicate glass can be deposited in the remaining volumes of the annular lateral recesses 149 after removal of the vertical stack of metal-semiconductor alloy portions 67. In one embodiment, the dielectric fill material may have a higher etch rate than the material of the blocking dielectric layer 52. For example, the dielectric fill material may include borosilicate glass, which can provide an etch rate in dilute hydrofluoric acid than the etch rate of undoped silicate glass by a factor in a range from 100 to 10,000.

Portions of the dielectric fill material can be removed from outside the annular lateral recesses 149 by etching back the dielectric fill material. An isotropic etch process or an anisotropic etch process may be employed. The chemistry of the etch process employed to etch the dielectric fill material can be selective to the material of the semiconductor material portions 54S and the material of the blocking dielectric layer 52. Remaining portions of the dielectric fill material filling the annular lateral recesses 149 comprise a vertical stack of annular insulating material portions 57. In case an anisotropic etch process is employed to pattern the annular insulating material portions 57, inner sidewalls of the annular insulating material portions 57 may be vertically coincident with inner sidewalls of the semiconductor material portions 54S.

Referring to FIG. 10O, the processing steps of FIGS. 10H-10M can be performed to provide an alternative configuration of the second exemplary memory opening fill structure 58. In this case, the tunneling dielectric layer 56 can be formed directly on the vertical stack of annular insulating material portions 57. The memory film 50 can comprise the blocking dielectric layer 52, the vertical stack of semiconductor material portions 54S, the vertical stack of annular insulating material portions 57 (which can contact the vertical stack of semiconductor material portions 54S), and the tunneling dielectric layer 56.

FIGS. 11A-11G are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of a seventh exemplary memory opening fill structure containing discrete dielectric charge storage elements with flange portions according to an embodiment of the present disclosure. The seventh exemplary memory opening fill structure can be formed within each memory opening 49 in lieu of the first, second, third, fourth, fifth, or sixth exemplary memory opening fill structure described above.

Referring to FIG. 11A, the structure for forming a seventh exemplary memory opening fill structure can be derived from the structure of FIG. 10G by nitriding the vertical stack of semiconductor material portions 54S. The vertical stack of semiconductor material portions 54S is fully converted into a vertical stack of silicon nitride material portions 54N. Each of the silicon nitride material portions 54N comprises a tubular portion 54T, an upper flange portion 54U laterally extending into the recess 149 outward from an upper end of an outer sidewall of the tubular portion 54T, and a lower flange portion 54F laterally extending into the recess 149 outward from a lower end of the outer sidewall of the tubular portion 54T. In one embodiment, each silicon nitride material portion 54N has a graded silicon-to-nitrogen ratio, as described with respect to FIG. 8A above. In one embodiment, the thickness of the tubular portion 54T of each silicon nitride material portion 54N can be in a range from 3 nm to 30 nm, such as from 5 nm to 15 nm, although lesser and greater thicknesses can also be employed. In one embodiment, the tubular portion 54T, the upper flange portion 54U, and the lower flange portion 54F can have substantially the same thickness.

The vertical stack of silicon nitride material portions 54N is located at levels of the spacer material layers (such as the sacrificial material layers 42). In one embodiment, each of the silicon nitride material portions 54N comprises a tubular portion 54T, an upper flange portion 54U, and a lower flange portion 54F. The upper flange portion 54U and the lower flange portion 54F of each silicon nitride material portion 54N provide increased charge trapping volume in additional to the charge trapping volume provided by the tubular portion 54T. Thus, the thickness of the spacer material layers (such as the sacrificial material layers 42) can be reduced relative to conventional NAND devices in which charge storage elements do not include flange portions. The vertical stack of discrete silicon nitride material portions 54N can be subsequently employed as a vertical stack of charge storage elements, which can function as floating gates of a NAND string. Portions of the inner sidewall of the blocking dielectric layer 52 are physically exposed after removal of the vertical stack of metal-semiconductor alloy portions 67.

Referring to FIG. 11B, the processing steps of FIG. 10H can be performed to form a tunneling dielectric layer 56.

Referring to FIG. 11C, the processing steps of FIG. 10I can be performed to form a first semiconductor channel layer 601.

Referring to FIG. 11D, the processing steps of FIG. 10J can optionally be performed to deposit the optional patterning film 77, and to anisotropically etch horizontal bottom portions of the first semiconductor channel layer 601 (if present), the tunneling dielectric layer 56, and the blocking dielectric layer 52 located over the pedestal channel portion 11 (or located above the upper substrate semiconductor layer 10 in case a pedestal channel portion is not present) at the bottom of each memory opening 49. A center portion of the top surface of the pedestal channel portion 11 can be vertically recessed by the anisotropic etch process. In case a pedestal channel portion 11 is not present in the memory opening 49, a portion of the horizontal surface of the upper substrate semiconductor layer 10 can be vertically recessed underneath the memory opening 49. The patterning film 77 (if present) can be subsequently removed, for example, by ashing.

Referring to FIG. 11E, the processing steps of FIG. 10K can be performed to form a second semiconductor channel layer 602. The materials of the first semiconductor channel layer 601 and the second semiconductor channel layer 602 are collectively referred to as a semiconductor channel material. The combination of the blocking dielectric layer 52, the tunneling dielectric layer 56, the first semiconductor channel layer 601, and the second semiconductor channel layer 602 can completely fill the volumes of the annular lateral recesses provided at the levels of the insulating layers 32.

Referring to FIG. 11F, the processing steps of FIG. 10L can be performed to form a dielectric core 62 in each memory opening 49.

Referring to FIG. 11G, the processing steps of FIG. 10M can be performed to form a doped semiconductor portion such as a drain region 63 at an upper portion of each memory opening 49. Each adjoining pair of a first semiconductor channel layer 601 and a second semiconductor channel layer 602 can collectively form a vertical semiconductor channel 60 through which electrical current can flow when a vertical NAND device including the vertical semiconductor channel 60 is turned on. A tunneling dielectric layer 56 is surrounded by a vertical stack of silicon nitride material portions 54N, and laterally surrounds a portion of the vertical semiconductor channel 60. Each adjoining set of a tunneling dielectric layer 56, a vertical stack of silicon nitride material portions 54N, and a blocking dielectric layer 52 collectively constitute a memory film 50, which includes a vertical stack of memory elements that can store a respective data bit with a macroscopic retention time.

Each combination of a memory film 50 and a vertical semiconductor channel 60 within a memory opening 49 constitutes a memory stack structure 55. The memory stack structure 55 is a combination of a semiconductor channel 60, a tunneling dielectric layer 56, a plurality of memory elements comprising a vertical stack of silicon nitride material portions 54N, and a blocking dielectric layer 52. Each combination of a pedestal channel portion 11 (if present), a memory stack structure 55, a dielectric core 62, and a drain region 63 within a memory opening 49 is herein referred to as a memory opening fill structure 58. Each combination of a pedestal channel portion 11 (if present), a memory film 50, a vertical semiconductor channel 60, a dielectric core 62, and a drain region 63 within each support opening 19 fills the respective support openings 19, and constitutes a support pillar structure.

FIGS. 11H and 11I illustrate an alternative configuration of the fourth exemplary memory opening fill structure. Referring to FIG. 11H, the alternative configuration of the seventh exemplary memory opening fill structure can be derived from the structure illustrated in FIG. 10G by filling the annular lateral recesses 149 with a dielectric fill material. The processing steps of FIG. 10N can be employed to form a vertical stack of annular insulating material portions 57 in unfilled volumes of the annular lateral recesses of each memory opening 49.

Referring to FIG. 11I, the processing steps of FIGS. 10H-10M can be performed to provide an alternative configuration of the first exemplary memory opening fill structure 58. In this case, the tunneling dielectric layer 56 can be formed directly on the vertical stack of annular insulating material portions 57. The memory film 50 can comprise the blocking dielectric layer 52, the vertical stack of silicon nitride material portions 54N, the vertical stack of annular insulating material portions 57 (which can contact the vertical stack of silicon nitride material portions 54N), and the tunneling dielectric layer 56.

FIGS. 12A-12G are sequential schematic vertical cross-sectional views of a memory opening within the exemplary structure during formation of an eighth exemplary memory opening fill structure containing hybrid discrete chare storage structures including discrete dielectric charge storage portions and floating gates with flange portions, according to an embodiment of the present disclosure. The eighth exemplary memory opening fill structure can be formed within each memory opening 49 in lieu of the first, second, third, fourth, fifth, sixth, or seventh exemplary memory opening fill structure described above.

Referring to FIG. 12A, the structure for forming the eight exemplary memory opening fill structure can be derived from the structure of FIG. 10G by partially nitriding the vertical stack of semiconductor material portions 54S. Surface portions of the semiconductor material portions 54S that are physically exposed to the memory cavity 49′ are converted into silicon nitride material portions 54N, while underlying portions of the semiconductor material portions 54S that contact the blocking dielectric layer 52 remain as semiconductor material portions 54S. Thus, a vertical stack of silicon nitride material portions 54N is formed by the nitridation process, and the remaining vertical stack of semiconductor material portions 54S has a lesser volume than the vertical stack of semiconductor material portions 54S provided at the processing steps of FIG. 10G. A vertical stack of composite charge storage structures (54S, 54N) can be formed by converting surface portions of the vertical stack of discrete semiconductor material portions 54S into the silicon nitride material portions 54N. In one embodiment, each silicon nitride material portion 54N comprises an interfacial region located in proximity to a respective one of the discrete semiconductor material portions 54S and having a graded silicon-to-nitrogen ratio, as described above. Each of the composite charge storage structures (54S, 54N) comprises a respective semiconductor material portion 54S (which is a remaining portion of a respective one of the discrete semiconductor material portions 54S as provided at the processing steps of FIG. 10G) and a respective silicon nitride material portion 54N which is formed by nitridation of a surface portion of the respective one of the discrete semiconductor material portions 54S.

Each of the composite charge storage structures (54S, 54N) comprises a tubular portion 54T, an upper flange portion 54U laterally extending outward into the recess 149 from an upper end of an outer sidewall of the tubular portion 54T, and a lower flange portion 54F laterally extending outward into the recess 149 from a lower end of the outer sidewall of the tubular portion 54T. Each semiconductor material portion 54S includes a respective tubular portion, a respective upper flange portion, and a respective lower flange portion. Each silicon nitride material portion 54N includes a respective tubular portion, a respective upper flange portion, and a respective lower flange portion. The thickness of the tubular portion of each semiconductor material portion 54S can be in a range from 1 nm to 30 nm, such as from 2 nm to 20 nm, although lesser and greater thicknesses can also be employed. The thickness of the tubular portion of each silicon nitride material portion 54N can be in a range from 1 nm to 30 nm, such as from 2 nm to 20 nm, although lesser and greater thicknesses can also be employed. The thickness of each tubular portion of composite charge storage structure (54S, 54N) can be in a range from 3 nm to 30 nm, such as from 5 nm to 15 nm, although lesser and greater thicknesses can also be employed. The thickness of a tubular portion of a composite charge storage structure (54S, 54N) can be formed between an inner cylindrical sidewall and an outer cylindrical sidewall of the respective composite charge storage structure (54S, 54N).

The vertical stack composite charge storage structures (54S, 54N) is located at levels of the spacer material layers (such as the sacrificial material layers 42) and partially protrudes into the recesses 149. In one embodiment, each of the composite charge storage structures (54S, 54N) comprises a tubular portion 54T, an upper flange portion 54U, and a lower flange portion 54F. The upper flange portion 54U and the lower flange portion 54F of each composite charge storage structure (54S, 54N) provide increased charge trapping volume in additional to the charge trapping volume provided by the tubular portion 54T. Thus, the thickness of the spacer material layers (such as the sacrificial material layers 42) can be reduced relative to conventional NAND devices in which charge storage elements do not include flange portions. The vertical stack of composite charge storage structures (54S, 54N) can be subsequently employed as a vertical stack of charge storage elements, which can function as hybrid floating gates and charge trapping dielectric elements of a NAND string. Portions of the inner sidewall of the blocking dielectric layer 52 are physically exposed after removal of the vertical stack of metal-semiconductor alloy portions 67.

Referring to FIG. 12B, the processing steps of FIG. 10H can be performed to form a tunneling dielectric layer 56.

Referring to FIG. 12C, the processing steps of FIG. 10I can be performed to form the optional first semiconductor channel layer 601.

Referring to FIG. 12D, the processing steps of FIG. 10J can optionally be performed to deposit the optional patterning film 77, and to anisotropically etch horizontal bottom portions of the first semiconductor channel layer 601 (if present), the tunneling dielectric layer 56, and the blocking dielectric layer 52 located over the pedestal channel portion 11 (or located above the upper substrate semiconductor layer 10 in case a pedestal channel portion is not present) at the bottom of each memory opening 49. A center portion of the top surface of the pedestal channel portion 11 can be vertically recessed by the anisotropic etch process. In case a pedestal channel portion 11 is not present in the memory opening 49, a portion of the horizontal surface of the upper substrate semiconductor layer 10 can be vertically recessed underneath the memory opening 49. The patterning film 77 can be subsequently removed, for example, by ashing.

Referring to FIG. 12E, the processing steps of FIG. 10K can be performed to form a second semiconductor channel layer 602. The materials of the first semiconductor channel layer 601 and the second semiconductor channel layer 602 are collectively referred to as a semiconductor channel material. The combination of the blocking dielectric layer 52, the tunneling dielectric layer 56, the first semiconductor channel layer 601, and the second semiconductor channel layer 602 can completely fill the volumes of the annular lateral recesses provided at the levels of the insulating layers 32.

Referring to FIG. 12F, the processing steps of FIG. 10L can be performed to form a dielectric core 62 in each memory opening 49.

Referring to FIG. 12G, the processing steps of FIG. 10M can be performed to form a doped semiconductor portion such as a drain region 63 at an upper portion of each memory opening 49. Each adjoining pair of a first semiconductor channel layer 601 and a second semiconductor channel layer 602 can collectively form a vertical semiconductor channel 60 through which electrical current can flow when a vertical NAND device including the vertical semiconductor channel 60 is turned on. A tunneling dielectric layer 56 is surrounded by a vertical stack of composite charge storage structures (54S, 54N), and laterally surrounds a portion of the vertical semiconductor channel 60. Each adjoining set of a tunneling dielectric layer 56, a vertical stack of composite charge storage structures (54S, 54N), and a blocking dielectric layer 52 collectively constitute a memory film 50, which includes a vertical stack of memory elements that can store a respective data bit with a macroscopic retention time.

Each combination of a memory film 50 and a vertical semiconductor channel 60 within a memory opening 49 constitutes a memory stack structure 55. The memory stack structure 55 is a combination of a semiconductor channel 60, a tunneling dielectric layer 56, a plurality of memory elements comprising a vertical stack of composite charge storage structures (54S, 54N), and a blocking dielectric layer 52. Each combination of a pedestal channel portion 11 (if present), a memory stack structure 55, a dielectric core 62, and a drain region 63 within a memory opening 49 is herein referred to as a memory opening fill structure 58. Each combination of a pedestal channel portion 11 (if present), a memory film 50, a vertical semiconductor channel 60, a dielectric core 62, and a drain region 63 within each support opening 19 fills the respective support openings 19, and constitutes a support pillar structure.

FIGS. 12H and 12I illustrate an alternative configuration of the fourth exemplary memory opening fill structure. Referring to FIG. 12H, the alternative configuration of the fourth exemplary memory opening fill structure can be derived from the structure illustrated in FIG. 10G by filling the annular lateral recesses 149 with a dielectric fill material. The processing steps of FIG. 10N can be employed to form a vertical stack of annular insulating material portions 57 in unfilled volumes of the annular lateral recesses of each memory opening 49.

Referring to FIG. 12I, the processing steps of FIGS. 10H-10M can be performed to provide an alternative configuration of the first exemplary memory opening fill structure 58. In this case, the tunneling dielectric layer 56 can be formed directly on the vertical stack of annular insulating material portions 57. The memory film 50 can comprise the blocking dielectric layer 52, the vertical stack of composite charge storage structures (54S, 54N), the vertical stack of annular insulating material portions 57 (which can contact the vertical stack of silicon nitride material portions 54N), and the tunneling dielectric layer 56.

Referring to FIG. 13, the exemplary structure is illustrated after formation of memory opening fill structures 58 and support pillar structure 20 within the memory openings 49 and the support openings 19, respectively. An instance of a memory opening fill structure 58 can be formed within each memory opening 49 of the structure of FIGS. 4A and 4B. An instance of the support pillar structure 20 can be formed within each support opening 19 of the structure of FIGS. 4A and 4B.

Each memory stack structure 55 includes a vertical semiconductor channel 60, which may comprise multiple semiconductor channel layers (601, 602), and a memory film 50. The memory film 50 may comprise a tunneling dielectric layer 56 laterally surrounding the vertical semiconductor channel 60, a vertical stack of charge storage regions (comprising a charge storage layer 54) laterally surrounding the tunneling dielectric layer 56, and an optional blocking dielectric layer 52. While the present disclosure is described employing the illustrated configuration for the memory stack structure, the methods of the present disclosure can be applied to alternative memory stack structures including different layer stacks or structures for the memory film 50 and/or for the vertical semiconductor channel 60.

Referring to FIGS. 14A and 14B, a contact level dielectric layer 73 can be formed over the alternating stack (32, 42) of insulating layer 32 and sacrificial material layers 42, and over the memory stack structures 55 and the support pillar structures 20. The contact level dielectric layer 73 includes a dielectric material that is different from the dielectric material of the sacrificial material layers 42. For example, the contact level dielectric layer 73 can include silicon oxide. The contact level dielectric layer 73 can have a thickness in a range from 50 nm to 500 nm, although lesser and greater thicknesses can also be employed.

A photoresist layer (not shown) can be applied over the contact level dielectric layer 73, and is lithographically patterned to form openings in areas between clusters of memory stack structures 55. The pattern in the photoresist layer can be transferred through the contact level dielectric layer 73, the alternating stack (32, 42) and/or the retro-stepped dielectric material portion 65 employing an anisotropic etch to form backside trenches 79, which vertically extend from the top surface of the contact level dielectric layer 73 at least to the top surface of the substrate (9, 10), and laterally extend through the memory array region 100 and the staircase region 300.

In one embodiment, the backside trenches 79 can laterally extend along a first horizontal direction hd1 and can be laterally spaced apart among one another along a second horizontal direction hd2 that is perpendicular to the first horizontal direction hd1. The memory stack structures 55 can be arranged in rows that extend along the first horizontal direction hd1. The drain select level isolation structures 72 can laterally extend along the first horizontal direction hd1. Each backside trench 79 can have a uniform width that is invariant along the lengthwise direction (i.e., along the first horizontal direction hd1). Each drain select level isolation structure 72 can have a uniform vertical cross-sectional profile along vertical planes that are perpendicular to the first horizontal direction hd1 that is invariant with translation along the first horizontal direction hd1. Multiple rows of memory stack structures 55 can be located between a neighboring pair of a backside trench 79 and a drain select level isolation structure 72, or between a neighboring pair of drain select level isolation structures 72. In one embodiment, the backside trenches 79 can include a source contact opening in which a source contact via structure can be subsequently formed. The photoresist layer can be removed, for example, by ashing.

Dopants of the second conductivity type can be implanted into portions of the upper substrate semiconductor layer 10 that underlie the backside trenches 79 to form source regions 61. The atomic concentration of the dopants of the second conductivity type in the source regions 61 can be in a range from 5.0×10¹⁸/cm³ to 2.0×10²¹/cm³, although lesser and greater atomic concentrations can also be employed. Surface portions of the upper substrate semiconductor layer 10 that extend between each source region 61 and adjacent memory opening fill structures 58 comprise horizontal semiconductor channels 59.

Referring to FIG. 15, an etchant that selectively etches the spacer material of the sacrificial material layers 42 with respect to the insulating material of the insulating layers 32 can be introduced into the backside trenches 79, for example, employing an etch process. Backside recesses 43 are formed in volumes from which the sacrificial material layers 42 are removed. The removal of the spacer material of the sacrificial material layers 42 can be selective to the insulating material of the insulating layers 32, the material of the retro-stepped dielectric material portion 65, the semiconductor material of the upper substrate semiconductor layer 10, and the material of the outermost layer of the memory films 50. In one embodiment, the sacrificial material layers 42 can include silicon nitride, and the materials of the insulating layers 32 and the retro-stepped dielectric material portion 65 can be selected from silicon oxide and dielectric metal oxides.

The etch process that removes the spacer material selective to the insulating material and the outermost layer of the memory films 50 can be a wet etch process employing a wet etch solution, or can be a gas phase (dry) etch process in which the etchant is introduced in a vapor phase into the backside trenches 79. For example, if the sacrificial material layers 42 include silicon nitride, the etch process can be a wet etch process in which the exemplary structure is immersed within a wet etch tank including phosphoric acid, which etches silicon nitride selective to silicon oxide, silicon, and various other materials employed in the art. The support pillar structures 20, the retro-stepped dielectric material portion 65, and the memory stack structures 55 provide structural support while the backside recesses 43 are present within volumes previously occupied by the sacrificial material layers 42.

Each backside recess 43 can be a laterally extending cavity having a lateral dimension that is greater than the vertical extent of the cavity. In other words, the lateral dimension of each backside recess 43 can be greater than the height of the backside recess 43. A plurality of backside recesses 43 can be formed in the volumes from which the spacer material of the sacrificial material layers 42 is removed. The memory openings in which the memory stack structures 55 are formed are herein referred to as front side openings or front side cavities in contrast with the backside recesses 43. In one embodiment, the memory array region 100 comprises an array of monolithic three-dimensional NAND strings having a plurality of device levels disposed above the substrate (9, 10). In this case, each backside recess 43 can define a space for receiving a respective word line of the array of monolithic three-dimensional NAND strings.

Each of the plurality of backside recesses 43 can extend substantially parallel to the top surface of the substrate (9, 10). A backside recess 43 can be vertically bounded by a top surface of an underlying insulating layer 32 and a bottom surface of an overlying insulating layer 32. In one embodiment, each backside recess 43 can have a uniform height throughout.

Referring to FIGS. 16A and 16B, physically exposed surface portions of the optional pedestal channel portions 11 and the upper substrate semiconductor layer 10 can be converted into dielectric material portions by thermal conversion and/or plasma conversion of the semiconductor materials into dielectric materials. For example, thermal conversion and/or plasma conversion can be employed to convert a surface portion of each pedestal channel portion 11 into a tubular dielectric spacer 116, and to convert each physically exposed surface portion of the upper substrate semiconductor layer 10 into a planar dielectric portion (not illustrated). In one embodiment, each tubular dielectric spacer 116 can be topologically homeomorphic to a torus, i.e., generally ring-shaped. As used herein, an element is topologically homeomorphic to a torus if the shape of the element can be continuously stretched without destroying a hole or forming a new hole into the shape of a torus. The tubular dielectric spacers 116 include a dielectric material that includes the same semiconductor element as the pedestal channel portions 11 and additionally includes at least one non-metallic element such as oxygen and/or nitrogen such that the material of the tubular dielectric spacers 116 is a dielectric material. In one embodiment, the tubular dielectric spacers 116 can include a dielectric oxide, a dielectric nitride, or a dielectric oxynitride of the semiconductor material of the pedestal channel portions 11. Dopants in the drain regions 63, the source regions 61, and the semiconductor channels 60 can be activated during the anneal process that forms the planar dielectric portions and the tubular dielectric spacers 116. Alternatively, an additional anneal process may be performed to active the electrical dopants in the drain regions 63, the source regions 61, and the semiconductor channels 60.

A backside blocking dielectric layer 44 can be optionally formed. The backside blocking dielectric layer 44, if present, comprises a dielectric material that functions as a control gate dielectric for the control gates to be subsequently formed in the backside recesses 43. In case the blocking dielectric layer 52 is present within each memory opening, the backside blocking dielectric layer 44 is optional. In case the blocking dielectric layer 52 is omitted, the backside blocking dielectric layer 44 is present.

The backside blocking dielectric layer 44 can be formed in the backside recesses 43 and on a sidewall of the backside trench 79. The backside blocking dielectric layer 44 can be formed directly on horizontal surfaces of the insulating layers 32 and sidewalls of the memory stack structures 55 within the backside recesses 43. If the backside blocking dielectric layer 44 is formed, formation of the tubular dielectric spacers 116 and the planar dielectric portion prior to formation of the backside blocking dielectric layer 44 is optional. In one embodiment, the backside blocking dielectric layer 44 can be formed by a conformal deposition process such as atomic layer deposition (ALD) or low pressure chemical vapor deposition (LPCVD). The backside blocking dielectric layer 44 can consist essentially of aluminum oxide. The thickness of the backside blocking dielectric layer 44 can be in a range from 1 nm to 15 nm, such as 2 to 6 nm, although lesser and greater thicknesses can also be employed.

The dielectric material of the backside blocking dielectric layer 44 can be a dielectric metal oxide such as aluminum oxide, a dielectric oxide of at least one transition metal element, a dielectric oxide of at least one Lanthanide element, a dielectric oxide of a combination of aluminum, at least one transition metal element, and/or at least one Lanthanide element. Alternatively or additionally, the backside blocking dielectric layer 44 can include a silicon oxide layer. The backside blocking dielectric layer 44 can be deposited by a conformal deposition method such as low pressure chemical vapor deposition or atomic layer deposition. The backside blocking dielectric layer 44 is formed on the sidewalls of the backside trenches 79, horizontal surfaces and sidewalls of the insulating layers 32, the portions of the sidewall surfaces of the memory stack structures 55 that are physically exposed to the backside recesses 43, and a top surface of the planar dielectric portion. A backside cavity is present within the portion of each backside trench 79 that is not filled with the backside blocking dielectric layer 44.

At least one metallic material can be deposited in the backside recesses 43. For example, a combination of a metallic barrier layer and a metallic fill material can be deposited in the backside recesses 43. The metallic barrier layer includes an electrically conductive metallic material that can function as a diffusion barrier layer and/or adhesion promotion layer for a metallic fill material to be subsequently deposited. The metallic barrier layer can include a conductive metallic nitride material such as TiN, TaN, WN, MoN, or a stack thereof, or can include a conductive metallic carbide material such as TiC, TaC, WC, or a stack thereof. In one embodiment, the metallic barrier layer can be deposited by a conformal deposition process such as chemical vapor deposition (CVD) or atomic layer deposition (ALD). The thickness of the metallic barrier layer can be in a range from 2 nm to 8 nm, such as from 3 nm to 6 nm, although lesser and greater thicknesses can also be employed. In one embodiment, the metallic barrier layer can consist essentially of a conductive metal nitride such as TiN. The metallic fill material can be deposited by a conformal deposition method, which can be, for example, chemical vapor deposition (CVD), atomic layer deposition (ALD), electroless plating, electroplating, or a combination thereof. In one embodiment, the metallic fill material layer can consist essentially of at least one elemental metal. The at least one elemental metal of the metallic fill material layer can be selected, for example, from tungsten, molybdenum, cobalt, ruthenium, titanium, and tantalum. In one embodiment, the metallic fill material layer can consist essentially of a single elemental metal. In one embodiment, the metallic fill material layer can be deposited employing a fluorine-containing precursor gas such as WF₆. In one embodiment, the metallic fill material layer can be a tungsten layer including a residual level of fluorine atoms as impurities. The metallic fill material layer is spaced from the insulating layers 32 and the memory stack structures 55 by the metallic barrier layer, which can block diffusion of fluorine atoms therethrough.

A plurality of electrically conductive layers 46 can be formed in the plurality of backside recesses 43, and a continuous electrically conductive material layer (not shown) can be formed on the sidewalls of each backside trench 79 and over the contact level dielectric layer 73. Each electrically conductive layer 46 includes a portion of the metallic barrier layer 46A and a portion of the metallic fill material layer 46B that are located between a vertically neighboring pair of dielectric material layers such as a pair of insulating layers 32. The continuous electrically conductive material layer includes a continuous portion of the at least one conductive material that is located in the backside trenches 79 or above the contact level dielectric layer 73.

Each sacrificial material layer 42 can be replaced with an electrically conductive layer 46. A backside cavity is present in the portion of each backside trench 79 that is not filled with the backside blocking dielectric layer 44 and the continuous electrically conductive material layer. A tubular dielectric spacer 116 laterally surrounds a pedestal channel portion 11. A bottommost electrically conductive layer 46 laterally surrounds each tubular dielectric spacer 116 upon formation of the electrically conductive layers 46.

The deposited metallic material of the continuous electrically conductive material layer is etched back from the sidewalls of each backside trench 79 and from above the contact level dielectric layer 73, for example, by an isotropic wet etch, an anisotropic dry etch, or a combination thereof. Each remaining portion of the deposited metallic material in the backside recesses 43 constitutes an electrically conductive layer 46. Each electrically conductive layer 46 can be a conductive line structure. Thus, the sacrificial material layers 42 are replaced with the electrically conductive layers 46.

Each electrically conductive layer 46 can function as a combination of a plurality of control gate electrodes located at a same level and a word line electrically interconnecting, i.e., electrically shorting, the plurality of control gate electrodes located at the same level. The plurality of control gate electrodes within each electrically conductive layer 46 are the control gate electrodes for the vertical memory devices including the memory stack structures 55. In other words, each electrically conductive layer 46 can be a word line that functions as a common control gate electrode for the plurality of vertical memory devices.

In one embodiment, the removal of the continuous electrically conductive material layer can be selective to the material of the backside blocking dielectric layer 44. In this case, a horizontal portion of the backside blocking dielectric layer 44 can be present at the bottom of each backside trench 79. In another embodiment, the removal of the continuous electrically conductive material layer may not be selective to the material of the backside blocking dielectric layer 44 or, the backside blocking dielectric layer 44 may not be employed. The planar dielectric portions can be removed during removal of the continuous electrically conductive material layer. A backside cavity is present within each backside trench 79.

Referring to FIG. 17, an insulating material layer can be formed in the backside trenches 79 and over the contact level dielectric layer 73 by a conformal deposition process. Exemplary conformal deposition processes include, but are not limited to, chemical vapor deposition and atomic layer deposition. The insulating material layer includes an insulating material such as silicon oxide, silicon nitride, a dielectric metal oxide, an organosilicate glass, or a combination thereof. In one embodiment, the insulating material layer can include silicon oxide. The insulating material layer can be formed, for example, by low pressure chemical vapor deposition (LPCVD) or atomic layer deposition (ALD). The thickness of the insulating material layer can be in a range from 1.5 nm to 60 nm, although lesser and greater thicknesses can also be employed.

If a backside blocking dielectric layer 44 is present, the insulating material layer can be formed directly on surfaces of the backside blocking dielectric layer 44 and directly on the sidewalls of the electrically conductive layers 46. If a backside blocking dielectric layer 44 is not employed, the insulating material layer can be formed directly on sidewalls of the insulating layers 32 and directly on sidewalls of the electrically conductive layers 46.

An anisotropic etch is performed to remove horizontal portions of the insulating material layer from above the contact level dielectric layer 73 and at the bottom of each backside trench 79. Each remaining portion of the insulating material layer constitutes an insulating spacer 74. A backside cavity is present within a volume surrounded by each insulating spacer 74. A top surface of the upper substrate semiconductor layer 10 can be physically exposed at the bottom of each backside trench 79.

An upper portion of the upper substrate semiconductor layer 10 that extends between the source region 61 and the plurality of pedestal channel portions 11 constitutes a horizontal semiconductor channel 59 for a plurality of field effect transistors. The horizontal semiconductor channel 59 is connected to multiple vertical semiconductor channels 60 through respective pedestal channel portions 11. The horizontal semiconductor channel 59 contacts the source region 61 and the plurality of pedestal channel portions 11. A bottommost electrically conductive layer 46 provided upon formation of the electrically conductive layers 46 within the alternating stack (32, 46) can comprise a select gate electrode for the field effect transistors. Each source region 61 is formed in an upper portion of the substrate (9, 10). Semiconductor channels (59, 11, 60) extend between each source region 61 and a respective set of drain regions 63. The semiconductor channels (59, 11, 60) include the vertical semiconductor channels 60 of the memory stack structures 55.

A backside contact via structure 76 can be formed within each backside cavity. Each contact via structure 76 can fill a respective backside cavity. The contact via structures 76 can be formed by depositing at least one conductive material in the remaining unfilled volume (i.e., the backside cavity) of the backside trench 79. For example, the at least one conductive material can include a conductive liner 76A and a conductive fill material portion 76B. The conductive liner 76A can include a conductive metallic liner such as TiN, TaN, WN, WC, TiC, TaC, MoN, an alloy thereof, or a stack thereof. The thickness of the conductive liner 76A can be in a range from 3 nm to 30 nm, although lesser and greater thicknesses can also be employed. The conductive fill material portion 76B can include a metal or a metallic alloy. For example, the conductive fill material portion 76B can include W, Mo, Cu, Al, Co, Ru, Ni, an alloy thereof, or a stack thereof.

In an alternative embodiment, the contact via structure 76 may be omitted and a horizontal source line may contact a side of a bottom portion of the vertical semiconductor channel 60.

The at least one conductive material can be planarized employing the contact level dielectric layer 73 overlying the alternating stack (32, 46) as a stopping layer. If chemical mechanical planarization (CMP) process is employed, the contact level dielectric layer 73 can be employed as a CMP stopping layer. Each remaining continuous portion of the at least one conductive material in the backside trenches 79 constitutes a backside contact via structure 76.

The backside contact via structure 76 extends through the alternating stack (32, 46), and contacts a top surface of the source region 61. If a backside blocking dielectric layer 44 is employed, the backside contact via structure 76 can contact a sidewall of the backside blocking dielectric layer 44.

Referring to FIGS. 18A and 18B, additional contact via structures (88, 86, 8P) can be formed through the contact level dielectric layer 73, and optionally through the retro-stepped dielectric material portion 65. For example, drain contact via structures 88 can be formed through the contact level dielectric layer 73 on each drain region 63. Word line contact via structures 86 can be formed on the electrically conductive layers 46 through the contact level dielectric layer 73, and through the retro-stepped dielectric material portion 65. Peripheral device contact via structures 8P can be formed through the retro-stepped dielectric material portion 65 directly on respective nodes of the peripheral devices.

The exemplary structures can include a three-dimensional memory device. In one embodiment, the three-dimensional memory device comprises a monolithic three-dimensional NAND memory device. The electrically conductive layers 46 can comprise, or can be electrically connected to, a respective word line of the monolithic three-dimensional NAND memory device. The substrate (9, 10) can comprise a silicon substrate. The vertical NAND memory device can comprise an array of monolithic three-dimensional NAND strings over the silicon substrate. The silicon substrate can contain an integrated circuit comprising a driver circuit (comprising a subset of the least one semiconductor device 700) for the memory device located thereon. Alternatively, the driver circuit may be formed on a separate substrate and then bonded to the memory device. The electrically conductive layers 46 can comprise a plurality of control gate electrodes having a strip shape extending substantially parallel to the top surface of the substrate (9, 10), e.g., between a pair of backside trenches 79. The plurality of control gate electrodes comprises at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level. The array of monolithic three-dimensional NAND strings can comprise: a plurality of semiconductor channels (59, 11, 60), wherein at least one end portion 60 of each of the plurality of semiconductor channels (59, 11, 60) extends substantially perpendicular to a top surface of the substrate (9, 10) and comprising a respective one of the vertical semiconductor channels 60, and a plurality of charge storage elements. Each charge storage element can be located adjacent to a respective one of the plurality of semiconductor channels (59, 11, 60).

FIG. 19A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a first exemplary memory opening fill structure or a second exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a semiconductor material portion 54S, which may have a tubular configuration. The tunneling dielectric layer 56 is in direct contact with the blocking dielectric layer 52 at levels of the insulating layers 32.

FIG. 19B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the first exemplary memory opening fill structure or the second exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a semiconductor material portion 54S, which may have a tubular configuration. The tunneling dielectric layer 56 is in direct contact with inner sidewalls of the annular insulating material portions 57 at levels of the insulating layers 32.

FIG. 20A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a third exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a combination of a semiconductor material portion 54S (which may have a tubular configuration) and a portion of a silicon nitride layer 53 located at the level of the semiconductor material portion 54S. The tunneling dielectric layer 56 is in direct contact with the blocking dielectric layer 52 at levels of the insulating layers 32.

FIG. 20B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the third exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a combination of a semiconductor material portion 54S (which may have a tubular configuration) and a portion of a silicon nitride layer 53 located at the level of the semiconductor material portion 54S. The tunneling dielectric layer 56 is in direct contact with inner sidewalls of the annular insulating material portions 57 at levels of the insulating layers 32.

FIG. 21A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a fourth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a discrete silicon nitride material portion 54N, which may have a tubular configuration. The tunneling dielectric layer 56 is in direct contact with the blocking dielectric layer 52 at levels of the insulating layers 32.

FIG. 21B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the fourth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a silicon nitride material portion 54N, which may have a tubular configuration. The tunneling dielectric layer 56 is in direct contact with inner sidewalls of the annular insulating material portions 57 at levels of the insulating layers 32.

FIG. 22A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a fifth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a discrete, composite charge storage structure (54S, 54N), which may have a tubular configuration. Each composite charge storage structure (54S, 54N) can include a stack of a semiconductor material portion 54S and a silicon nitride material portion 54N. The tunneling dielectric layer 56 is in direct contact with the blocking dielectric layer 52 at levels of the insulating layers 32.

FIG. 22B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the fifth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a composite charge storage structure (54S, 54N), which may have a tubular configuration. Each composite charge storage structure (54S, 54N) can include a stack of a semiconductor material portion 54S and a silicon nitride material portion 54N. The tunneling dielectric layer 56 is in direct contact with inner sidewalls of the annular insulating material portions 57 at levels of the insulating layers 32.

FIG. 23A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a sixth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a discrete semiconductor material portion 54S, which may have a tubular portion 54T, an upper flange portion 54U, and a lower flange portion 54F. The tunneling dielectric layer 56 is in direct contact with the blocking dielectric layer 52 at levels of the insulating layers 32.

FIG. 23B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the sixth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a semiconductor material portion 54S, which may have a tubular portion 54T, an upper flange portion 54U, and a lower flange portion 54F. The tunneling dielectric layer 56 is in direct contact with inner sidewalls of the annular insulating material portions 57 at levels of the insulating layers 32.

FIG. 24A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a seventh exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a discrete silicon nitride material portion 54N, which may have a tubular portion 54T, an upper flange portion 54U, and a lower flange portion 54F. The tunneling dielectric layer 56 is in direct contact with the blocking dielectric layer 52 at levels of the insulating layers 32.

FIG. 24B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the seventh exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a silicon nitride material portion 54N, which may have a tubular portion 54T, an upper flange portion 54U, and a lower flange portion 54F. The tunneling dielectric layer 56 is in direct contact with inner sidewalls of the annular insulating material portions 57 at levels of the insulating layers 32.

FIG. 25A is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case a eighth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a discrete composite charge storage structure (54S, 54N), which includes a stack of a semiconductor material portion 54S and a silicon nitride material portion 54N. Each composite charge storage structure (54S, 54N) may have a tubular portion 54T, an upper flange portion 54U, and a lower flange portion 54F. The tunneling dielectric layer 56 is in direct contact with the blocking dielectric layer 52 at levels of the insulating layers 32.

FIG. 25B is a magnified view of a memory opening in the exemplary structure of FIGS. 18A and 18B in case an alternative configuration of the eighth exemplary memory opening fill structure is present in the memory opening according to an embodiment of the present disclosure. In this case, each charge storage element may comprise a composite charge storage structure (54S, 54N), which includes a stack of a semiconductor material portion 54S and a silicon nitride material portion 54N. Each composite charge storage structure (54S, 54N) may have a tubular portion 54T, an upper flange portion 54U, and a lower flange portion 54F. The tunneling dielectric layer 56 is in direct contact with inner sidewalls of the annular insulating material portions 57 at levels of the insulating layers 32.

Referring to all drawings and according to various embodiments of the present disclosure, a three-dimensional memory device is provided, which comprises: an alternating stack of insulating layers 32 and electrically conductive layers 46 located over a substrate (9, 10); a memory opening 49 vertically extending through the alternating stack (32, 46), wherein the memory opening 49 has laterally-protruding portions (such as the annular lateral recesses 149) that extend outward at each level of the insulating layers 32; and a memory opening fill structure 58 located in the memory opening 49 and comprising, from outside to inside, a blocking dielectric layer 52, charge storage structures {(54S, 54N) or (54S, 52)} comprising a vertical stack of discrete semiconductor material portions 54S and at least one silicon nitride material portion (54N or 53) in contact with the vertical stack 54S, a tunneling dielectric layer 56 in contact with the charge storage structures {(54S, 54N) or (54S, 52)}, and a vertical semiconductor channel 60.

In one embodiment, the at least one silicon nitride material portion 54N comprises a vertical stack of discrete silicon nitride material portions 54N in contact with a respective discrete semiconductor material portion 54S within the vertical stack of discrete semiconductor material portions 54S.

In one embodiment, each discrete silicon nitride material portion 54N within the vertical stack of discrete silicon nitride material portions 54N is in contact with the tunneling dielectric layer 56; and each discrete semiconductor material portion 54S within the vertical stack of discrete semiconductor material portions 54S is not in contact with the tunneling dielectric layer 56, and is spaced from the tunneling dielectric layer 56 by the vertical stack of discrete silicon nitride material portions 54N.

In one embodiment, each silicon nitride material portion 54N comprises a tubular portion 54T having a uniform thickness between an inner sidewall and an outer sidewall, an upper flange portion 54U extending outward from an upper periphery of the inner sidewall of the tubular portion 54T, and a lower flange portion 54F extending outward from a lower periphery of the inner sidewall of the tubular portion 54T.

In one embodiment, each silicon nitride material portion 54N comprises an interfacial region located in proximity to a respective one of the discrete semiconductor material portions 54S and having a graded silicon-to-nitrogen ratio.

In one embodiment, the at least one silicon nitride material portion comprises a silicon nitride layer 53 vertically extending through layers of the alternating stack (32, 46) and contacting an outer sidewall of each discrete semiconductor material portion 54S within the vertical stack of discrete semiconductor material portions 54S. In one embodiment, the silicon nitride layer 53 is in contact with an inner sidewall of the blocking dielectric layer 52 and an outer sidewall of the tunneling dielectric layer 56. In one embodiment, all surfaces of the vertical stack of discrete semiconductor material portions 54S are in contact with a surface of the silicon nitride liner 53 or a surface of the tunneling dielectric layer 56.

In one embodiment, the tunneling dielectric layer 56 has a laterally-undulating vertical cross-sectional profile, and comprises laterally-protruding portions located at levels of the insulating layers 32 and contacting horizontal annular surfaces of the blocking dielectric layer 52 and overlying or underlying portions of the electrically conductive layers 46 that are proximal to the vertical stack of discrete semiconductor material portions 54S.

In one embodiment, the memory opening fill structure 58 comprises a vertical stack of annular insulating material portions 57 located at each level of the insulating layers 32 between the blocking dielectric layer 52 and the tunneling dielectric layer 56; and the tunneling dielectric layer 56 comprises a straight outer sidewall contacting each annular insulating material portion 57 within the vertical stack of annular insulating material portions 57 and contacting the vertical stack of discrete semiconductor material portions 54S.

According to another aspect of the present disclosure, a three-dimensional memory device is provided, which comprises: an alternating stack of insulating layers 32 and electrically conductive layers 46 located over a substrate (9, 10); a memory opening 49 vertically extending through the alternating stack (32, 46), wherein the memory opening 49 has laterally-protruding portions (such as the annular lateral recesses 149) that extend outward at levels of the insulating layers 32; and a memory opening fill structure 58 located in the memory opening 49 and comprising, from outside to inside, a blocking dielectric layer 52, a vertical stack of discrete charge storage material portions {54S, 54N, (54S, 54N)}, a tunneling dielectric layer 56, and a vertical semiconductor channel 60, wherein each charge storage material portion {54S, 54N, (54S, 54N)} comprises a tubular portion 54T located at a level of a respective one of the electrically material layers 46, an upper flange portion 54U laterally extending outward from an upper end of an outer sidewall of the tubular portion 54T, and a lower flange portion 54F laterally extending outward from a lower end of the outer sidewall of the tubular portion 54T.

In one embodiment, each charge storage material portion comprises a respective semiconductor material portion 54S. In one embodiment, each charge storage material portion comprises a respective silicon nitride material portion 54N. In one embodiment, each charge storage material portion comprises a respective stack of a semiconductor material portion 54S and a silicon nitride material portion 54N. In one embodiment, the semiconductor material portion 54S of each charge storage material portion (54S, 54N) does not contact the tunneling dielectric layer 56, and is spaced from the tunneling dielectric layer 56 by a respective one of the silicon nitride material portions 54N.

In one embodiment, the upper flange portion 54U contacts a horizontal top surface of the blocking dielectric layer 52; and the lower flange portion 54F comprises a horizontal bottom surface of the blocking dielectric layer 52.

In one embodiment, the blocking dielectric layer 52 have a laterally-undulating vertical cross-sectional profile; first tubular portions of the blocking dielectric layer 52 located at levels of the insulating layers 32 are laterally offset outward from second tubular portions of the blocking dielectric layer 52 located at levels of the electrically conductive layers 46; and the first tubular portions of the blocking dielectric layer 52 are not in contact with (i.e., not in direct contact with) the vertical stack of charge storage material portions 54.

In one embodiment, the vertical semiconductor channel 60 comprises: a tubular portion that vertically extends through a plurality of electrically conductive material layers 46 within the alternating stack (32, 46); and laterally-protruding portions that protrude outward from the tubular portion at the levels of the insulating layers 32 (as illustrated, for example, in FIGS. 19A, 20A, 21A, 22A, 23A, 24A, and 25A).

In one embodiment, the memory opening fill structure 58 comprises a vertical stack of annular insulating material portions 57 located at the levels of the insulating layers 32 between the blocking dielectric layer 52 and the tunneling dielectric layer 56; and the tunneling dielectric layer 56 comprises a straight outer sidewall contacting each annular insulating material portion 57 within the vertical stack of annular insulating material portions 57 and contacting the vertical stack of charge storage material portions {54S, 54N, (54S, 54N)} (as illustrated in FIGS. 19B, 20B, 21B, 22B, 23B, 24B, and 25B).

In one embodiment, the memory opening fill structure 58 comprises a doped semiconductor material portion (such as a drain region 63) that overlies the vertical semiconductor channel 60 and forms a p-n junction at an interface with the vertical semiconductor channel 60.

The various embodiments of the present disclosure can be employed to provide a vertical stack of discrete charge storage elements providing reduced charge leakage across vertical levels and/or increased charge storage capacity through use of flange portions for each charge storage element. The various embodiments of the present disclosure can facilitate device scaling along the vertical direction in a three-dimensional NAND memory device or other vertical memory devices.

Although the foregoing refers to particular preferred embodiments, it will be understood that the disclosure is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the disclosure. Compatibility is presumed among all embodiments that are not alternatives of one another. The word “comprise” or “include” contemplates all embodiments in which the word “consist essentially of” or the word “consists of” replaces the word “comprise” or “include,” unless explicitly stated otherwise. Where an embodiment employing a particular structure and/or configuration is illustrated in the present disclosure, it is understood that the present disclosure may be practiced with any other compatible structures and/or configurations that are functionally equivalent provided that such substitutions are not explicitly forbidden or otherwise known to be impossible to one of ordinary skill in the art. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety. 

What is claimed is:
 1. A method of forming a three-dimensional memory device, comprising: forming an alternating stack of insulating layers and spacer material layers over a substrate, wherein the spacer material layers are formed as, or are subsequently replaced with, electrically conductive layers; forming a memory opening through the alternating stack; forming annular lateral recesses at levels of the insulating layers by laterally recessing sidewalls of the insulating layers relative to sidewalls of the spacer material layers around the memory opening; forming a vertical stack of discrete metal portions in the annular lateral recesses; forming a semiconductor material layer on the vertical stack of the metal portions; forming a vertical stack of metal-semiconductor alloy portions by reacting the vertical stack of metal portions with portions of the semiconductor material layer located at levels of the insulating layers; removing the vertical stack of metal-semiconductor alloy portions selective to unreacted portions of the semiconductor material layer, wherein unreacted portions of the semiconductor material layer remain at levels of the spacer material layers and comprise a vertical stack of discrete semiconductor material portions; and forming a tunneling dielectric layer and a vertical semiconductor channel in the memory opening.
 2. The method of claim 1, wherein the tunneling dielectric layer is formed directly on the vertical stack of discrete semiconductor material portions.
 3. The method of claim 1, further comprising converting the vertical stack of discrete semiconductor material portions into a vertical stack of discrete cylindrical silicon nitride material portions by performing a nitridation process prior to formation of the tunneling dielectric layer.
 4. The method of claim 1, further comprising forming a vertical stack of discrete composite charge storage structures by converting surface portions of the vertical stack of discrete semiconductor material portions into silicon nitride material portions, wherein each of the discrete composite charge storage structures comprises a respective semiconductor material portion which is a remaining portion of a respective one of the discrete semiconductor material portions and a respective silicon nitride material portion which is formed by nitridation of a surface portion of the respective one of the discrete semiconductor material portions.
 5. The method of claim 1, further comprising: forming a blocking dielectric layer on a sidewall of the memory opening after formation of the annular lateral recesses; conformally depositing a metal layer on an inner sidewalls of the blocking dielectric layer; and anisotropically etching portions of the metal layer located outside the annular lateral recesses, wherein remaining portions of the metal layer comprise the vertical stack of discrete metal portions.
 6. The method of claim 1, further comprising: forming a blocking dielectric layer on a sidewall of the memory opening after formation of the annular lateral recesses; conformally depositing a metal layer on an inner sidewalls of the blocking dielectric layer; and inducing thermal migration of the metal layer into the annular lateral recesses by performing an anneal process, wherein the metal layer self-segregates into the vertical stack of discrete metal portions during the anneal process.
 7. The method of claim 1, further comprising forming a silicon nitride layer on the blocking dielectric layer, wherein the vertical stack of discrete metal portions is formed on portions of an inner sidewall of the silicon nitride layer that are located at levels of the insulating layers, and wherein the tunneling dielectric layer is formed directly on the portions of the inner sidewall of the silicon nitride layer that are located at levels of the insulating layers after removal of the vertical stack of metal-semiconductor alloy portions.
 8. The method of claim 1, wherein: the vertical stack of discrete metal portions is formed directly on portions of an inner sidewall of a blocking dielectric layer located at levels of the insulating layers; and the portions of the inner sidewall of the blocking dielectric layer are physically exposed after removal of the vertical stack of metal-semiconductor alloy portions.
 9. The method of claim 8, wherein the tunneling dielectric layer is formed directly on the portions of the inner sidewall of the blocking dielectric layer located at the levels of the insulating layers.
 10. The method of claim 8, further comprising: filling the annular lateral recesses by depositing a dielectric fill material after removal of the vertical stack of metal-semiconductor alloy portions; and removing portions of the dielectric fill material from outside the annular lateral recesses by anisotropically etching the dielectric fill material, wherein remaining portions of the dielectric fill material filling the annular lateral recesses comprise a vertical stack of annular insulating material portions, and the tunneling dielectric layer is formed directly on the vertical stack of annular insulating material portions. 